Guidelines for Cryptography

Cryptographic fundamentals

Purpose of cryptography

The purpose of cryptography is to provide confidentiality, integrity, authentication and non-repudiation of data. In doing so, confidentiality protects data by making it unreadable to all but authorised entities, integrity protects data from accidental or deliberate manipulation by entities, authentication ensures that an entity is who they claim to be, and non-repudiation provides proof that an entity performed a particular action.

Using encryption

Encryption of data at rest can be used to protect sensitive or classified data stored on information technology (IT) equipment and media. In addition, encryption of data in transit can be used to protect sensitive or classified data communicated over public network infrastructure. However, when an organisation uses encryption for data at rest, or data in transit, they are not reducing the sensitivity or classification of the data, they are simply reducing the immediate consequences of the data being accessed by malicious actors.

International standards for cryptographic modules

International Organization for Standardization (ISO)/International Electrotechnical Commission (IEC) 19790:2012, Information technology – Security techniques – Security requirements for cryptographic modules, and ISO/IEC 24759:2017, Information technology – Security techniques – Test requirements for cryptographic modules, are international standards for the design and validation of hardware and software cryptographic modules.

Federal Information Processing Standard (FIPS) 140-3, Security Requirements for Cryptographic Modules and National Institute of Standards and Technology (NIST) Special Publication (SP) 180-140, FIPS 140-3 Derived Test Requirements (DTR): CMVP Validation Authority Updates to ISO/IEC 24759 are United States standards based upon ISO/IEC 19790:2012 and ISO/IEC 24759:2017.

Communications security doctrine

The Australian Signals Directorate (ASD) specifies additional communications security requirements in Australian Communications Security Instructions that must be complied with when operating High Assurance Cryptographic Equipment (HACE). Such requirements supplement these guidelines and, where conflicts occur, take precedence.

Control: ISM-0499; Revision: 11; Updated: Sep-23; Applicability: S, TS; Essential Eight: N/A
Communications security doctrine produced by ASD for the management and operation of HACE is complied with.

Approved High Assurance Cryptographic Equipment

In order to ensure interoperability and maintain trust, all HACE must be issued an Approval for Use by ASD and be operated in accordance with the latest version of their associated Australian Communications Security Instructions.

Control: ISM-1802; Revision: 1; Updated: Sep-23; Applicability: S, TS; Essential Eight: N/A
HACE are issued an Approval for Use by ASD and operated in accordance with the latest version of their associated Australian Communications Security Instructions.

Cryptographic key management processes and procedures

Well documented cryptographic key management processes and procedures can assist with the secure use and management of cryptographic keys and associated hardware and software. In doing so, cryptographic key management processes and procedures should cover cryptographic key generation, registration, distribution, installation, usage, protection, storage, access, recovery and destruction.

Control: ISM-0507; Revision: 5; Updated: Dec-22; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
Cryptographic key management processes, and supporting cryptographic key management procedures, are developed, implemented and maintained.

Encrypting data at rest

When encryption is applied to data at rest it provides an additional layer of defence against unauthorised access by malicious actors. In doing so, it is important that full disk encryption is used as it provides a greater level of protection than file-based encryption. This is due to the fact that while file-based encryption may encrypt individual files, there is the possibility that unencrypted copies of files may be left in temporary locations used by an operating system. When selecting cryptographic equipment or software for this purpose, the level of assurance required will depend on the sensitivity or classification of the data.

Control: ISM-1080; Revision: 5; Updated: Jun-22; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
An ASD-Approved Cryptographic Algorithm (AACA) or high assurance cryptographic algorithm is used when encrypting media.

Control: ISM-0457; Revision: 9; Updated: Mar-22; Applicability: OS, P; Essential Eight: N/A
Cryptographic equipment or software that has completed a Common Criteria evaluation against a Protection Profile is used when encrypting media that contains OFFICIAL: Sensitive or PROTECTED data.

Control: ISM-0460; Revision: 13; Updated: Sep-23; Applicability: S, TS; Essential Eight: N/A
HACE is used when encrypting media that contains SECRET or TOP SECRET data.

Control: ISM-0459; Revision: 4; Updated: Dec-21; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
Full disk encryption, or partial encryption where access controls will only allow writing to the encrypted partition, is implemented when encrypting data at rest.

Encrypting data in transit

When data is communicated over network infrastructure, encryption should be used to protect the data from unauthorised access or manipulation. When selecting cryptographic equipment or software for this purpose, the level of assurance required will depend on the sensitivity or classification of the data and the environment in which it is being applied.

Control: ISM-0469; Revision: 6; Updated: Jun-22; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
An ASD-Approved Cryptographic Protocol (AACP) or high assurance cryptographic protocol is used to protect data when communicated over network infrastructure.

Control: ISM-0465; Revision: 9; Updated: Mar-22; Applicability: OS, P; Essential Eight: N/A
Cryptographic equipment or software that has completed a Common Criteria evaluation against a Protection Profile is used to protect OFFICIAL: Sensitive or PROTECTED data when communicated over insufficiently secure networks, outside of appropriately secure areas or via public network infrastructure.

Control: ISM-0467; Revision: 12; Updated: Sep-23; Applicability: S, TS; Essential Eight: N/A
HACE is used to protect SECRET and TOP SECRET data when communicated over insufficiently secure networks, outside of appropriately secure areas or via public network infrastructure.

Data recovery

To ensure that access to encrypted data is not lost due to the loss, damage or failure of an encryption key, it is important that where practical cryptographic equipment and software provides a means of data recovery.

Control: ISM-0455; Revision: 3; Updated: Mar-22; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
Where practical, cryptographic equipment and software provides a means of data recovery to allow for circumstances where the encryption key is unavailable due to loss, damage or failure.

Handling encrypted IT equipment and media

When a user authenticates to the encryption functionality of IT equipment or media, encrypted data is made available. At such a time, the IT equipment or media should be handled according to its original sensitivity or classification. Once the user deauthenticates from the encryption functionality, such as shutting down a device or activating a lock screen, the IT equipment or media can be considered to be protected by the encryption functionality again.

Control: ISM-0462; Revision: 8; Updated: Jun-24; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
When a user authenticates to the encryption functionality of IT equipment or media, it is treated in accordance with its original sensitivity or classification until the user deauthenticates from the encryption functionality.

Transporting cryptographic equipment

Transporting cryptographic equipment in a keyed state may expose its keying material to potential compromise. Therefore, if cryptographic equipment is transported in a keyed state, it should be done based on the sensitivity or classification of its keying material.

Control: ISM-0501; Revision: 6; Updated: Mar-22; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
Keyed cryptographic equipment is transported based on the sensitivity or classification of its keying material.

Reporting cryptographic-related cyber security incidents

If cryptographic equipment or associated keying material is compromised, or suspected of being compromised, then the confidentiality and integrity of previous and future communications may also be compromised. In such cases, the cyber security incident should be reported to the Chief Information Security Officer, or one of their delegates, as soon as possible after it occurs, and all keying material should be changed.

Control: ISM-0142; Revision: 5; Updated: Jun-23; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
The compromise or suspected compromise of cryptographic equipment or associated keying material is reported to the Chief Information Security Officer, or one of their delegates, as soon as possible after it occurs.

Control: ISM-1091; Revision: 6; Updated: Dec-21; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
Keying material is changed when compromised or suspected of being compromised.

Further information

Further information on cryptographic key management practices can be found in NIST SP 800-57 Part 1 Rev. 5, Recommendation for Key Management: Part 1 – General.

Further information on cryptographic key management practices for HACE is available from ASD.

Further information on cyber supply chain risk management can be found in the cyber supply chain risk management section of the Guidelines for Procurement and Outsourcing.

Further information on evaluated products can be found in the evaluated product procurement section of the Guidelines for Evaluated Products.

Further information on the evaluation of cryptographic modules, including testing requirements, is available as part of the Cryptographic Module Validation Program which is jointly operated by NIST and the Canadian Centre for Cyber Security.

Further information on the protection of IT equipment and media can be found in the Department of Home Affairs’ Protective Security Policy Framework.

ASD-Approved Cryptographic Algorithms

High assurance cryptographic algorithms

High assurance cryptographic algorithms, which are not covered in this section, can be used for the protection of SECRET and TOP SECRET data if they are suitably implemented in HACE. Further information on high assurance cryptographic algorithms can be obtained from ASD.

ASD-Approved Cryptographic Algorithms

There is no guarantee of a cryptographic algorithm’s resistance to currently unknown attacks. However, the cryptographic algorithms listed in this section have been extensively scrutinised by industry and academic communities in a practical and theoretical setting. Approval for the use of the cryptographic algorithms listed in this section is limited to cases where they are implemented in accordance with these guidelines.

The approved asymmetric cryptographic algorithms are:

• Diffie-Hellman (DH) for agreeing on encryption session keys
• Elliptic Curve Diffie-Hellman (ECDH) for agreeing on encryption session keys
• Elliptic Curve Digital Signature Algorithm (ECDSA) for digital signatures
• Module-Lattice-Based Digital Signature Algorithm (ML-DSA) for digital signatures
• Module-Lattice-Based Key Encapsulation Mechanism (ML-KEM) for encapsulating encryption session keys (and similar keys)
• Rivest-Shamir-Adleman (RSA) for digital signatures and transporting encryption session keys (and similar keys).

The only approved hashing algorithm for general purpose use is Secure Hashing Algorithm 2 (SHA-2). However, Secure Hashing Algorithm 3 (SHA-3), including its extendable-output functions (XOFs), is approved exclusively for use within ML-DSA and ML-KEM.

The only approved symmetric cryptographic algorithm is Advanced Encryption Standard (AES).

Where there is a range of key sizes for a cryptographic algorithm, some key sizes are not approved as they are insecure against current attacks or do not provide an adequate safety margin against possible future attacks. For example, advances in integer factorisation methods have rendered some RSA moduli sizes vulnerable and could render other RSA moduli vulnerable in the future.

The minimum targets used for the effective security strength of cryptographic algorithms listed within this section are:

• 112 bits for non-classified data
• 112 bits for OFFICIAL: Sensitive data
• 112 bits for PROTECTED data
• 128 bits for SECRET data
• 192 bits for TOP SECRET data.

Note, certain key sizes and parameters, such as specific elliptic curves, are preferred in order to promote interoperability with the United States’ Commercial National Security Algorithm Suite.

Using ASD-Approved Cryptographic Algorithms

If cryptographic equipment or software implements unapproved cryptographic algorithms, it is possible that these cryptographic algorithms could be used without a user’s knowledge. In combination with an assumed level of security confidence, this can represent a security risk. As such, an organisation can ensure that only AACAs or high assurance cryptographic algorithms can be used by disabling all unapproved cryptographic algorithms (preferred) or by advising users not to use the unapproved cryptographic algorithms via usage policies.

Control: ISM-0471; Revision: 7; Updated: Dec-21; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
Only AACAs or high assurance cryptographic algorithms are used by cryptographic equipment and software.

Asymmetric cryptographic algorithms

ECDH is vulnerable to different types of attacks than DH. Consequently, ECDH offers more effective security per bit increase in key size than DH. This leads to smaller data requirements, which in turn means that the elliptic curve variants have become de facto global standards. For reduced data cost, and to promote interoperability, ECDH should be used in preference to DH where possible.

Control: ISM-0994; Revision: 7; Updated: Mar-24; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
ECDH is used in preference to DH.

Using Diffie-Hellman

A modulus of 2048 bits for correctly implemented DH provides 112 bits of effective security strength, with larger modulus sizes providing more bits of effective security strength. However, taking into account projected technological advances in quantum computing, DH will not be approved for use beyond 2030.

When DH in a prime field is used, the prime modulus impacts the security of the cryptographic algorithm. The security considerations when creating such a prime modulus can be found in NIST SP 800-56A Rev. 3, along with a collection of commonly used secure moduli.

Control: ISM-0472; Revision: 7; Updated: Dec-24; Applicability: NC, OS, P; Essential Eight: N/A
When using DH for agreeing on encryption session keys, a modulus of at least 2048 bits is used, preferably 3072 bits.

Control: ISM-1759; Revision: 0; Updated: Mar-22; Applicability: S, TS; Essential Eight: N/A
When using DH for agreeing on encryption session keys, a modulus of at least 3072 bits is used, preferably 3072 bits.

Control: ISM-1629; Revision: 1; Updated: Dec-21; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
When using DH for agreeing on encryption session keys, a modulus and associated parameters are selected according to NIST SP 800-56A Rev. 3.

Using Elliptic Curve Cryptography

The curve used within an elliptic curve cryptographic algorithm impacts the security of the cryptographic algorithm. As such, only suitable curves from NIST SP 800-186 should be used.

Control: ISM-1446; Revision: 3; Updated: Mar-24; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
When using elliptic curve cryptography, a suitable curve from NIST SP 800-186 is used.

Using Elliptic Curve Diffie-Hellman

When identifying a suitable curve from NIST SP 800-186, a base point order and key size of at least 224 bits for correctly implemented ECDH provides 112 bits of effective security strength, with larger key sizes providing more bits of effective security strength. However, taking into account projected technological advances in quantum computing, ECDH will not be approved for use beyond 2030.

Note, security of a curve selected from another source cannot be assumed to have the same security using base point order and key size alone.

Control: ISM-0474; Revision: 7; Updated: Dec-24; Applicability: NC, OS, P; Essential Eight: N/A
When using ECDH for agreeing on encryption session keys, a base point order and key size of at least 224 bits is used, preferably the NIST P-384 curve.

Control: ISM-1761; Revision: 0; Updated: Mar-22; Applicability: S; Essential Eight: N/A
When using ECDH for agreeing on encryption session keys, NIST P-256, P-384 or P-521 curves are used, preferably the NIST P-384 curve.

Control: ISM-1762; Revision: 0; Updated: Mar-22; Applicability: TS; Essential Eight: N/A
When using ECDH for agreeing on encryption session keys, NIST P-384 or P-521 curves are used, preferably the NIST P-384 curve.

Using the Elliptic Curve Digital Signature Algorithm

When identifying a suitable curve from NIST SP 800-186, a base point order and key size of 224 bits for correctly implemented ECDSA provides 112 bits of effective security strength, with larger key sizes providing more bits of effective security strength. However, taking into account projected technological advances in quantum computing, ECDSA will not be approved for use beyond 2030.

Note, security of a curve selected from another source cannot be assumed to have the same security using base point order and key size alone.

Control: ISM-0475; Revision: 7; Updated: Dec-24; Applicability: NC, OS, P; Essential Eight: N/A
When using ECDSA for digital signatures, a base point order and key size of at least 224 bits is used, preferably the P-384 curve.

Control: ISM-1763; Revision: 0; Updated: Mar-22; Applicability: S; Essential Eight: N/A
When using ECDSA for digital signatures, NIST P-256, P-384 or P-521 curves are used, preferably the NIST P-384 curve.

Control: ISM-1764; Revision: 0; Updated: Mar-22; Applicability: TS; Essential Eight: N/A
When using ECDSA for digital signatures, NIST P-384 or P-521 curves are used, preferably the NIST P-384 curve.

Using post-quantum cryptographic algorithms

Post-quantum cryptographic algorithms are more complex than their traditional counterparts. To reduce the risk that vulnerabilities are introduced via implementation errors, approval is given to specific post-quantum cryptographic standards and their constituent post-quantum cryptographic algorithms.

Control: ISM-1990; Revision: 0; Updated: Dec-24; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
When using ML-DSA and ML-KEM, as per FIPS 204 and FIPS 203 respectively, adherence to pre-requisite FIPS publications is preferred.

Using the Module-Lattice-Based Digital Signature Algorithm

The effective security strength of ML-DSA has a complex dependency on numerous parameters with different effective security strengths targeted by different standardised parameter sets. The ML-DSA standard contains three different parameter sets: ML-DSA-44, ML-DSA-65 and ML-DSA-87. The use of ML-DSA-65 and ML-DSA-87 are approved for use. However, taking into account projected technological advances in quantum computing, ML-DSA-65 will not be approved for use beyond 2030.

When using ML-DSA for digital signing, it may either be hedged or deterministic. Notably, the hedged variant provides effective protection from certain side-channel attacks which apply to the deterministic variant. For this reason, the hedged variant should be used whenever possible. The deterministic variant should not be used unless the nature of the digital signing platform renders the creation of random data infeasible, which is a mandatory step for the hedged variant.

When using ML-DSA for digital signing, signing a message first involves hashing the message using SHAKE128 or SHAKE256. In environments where the message being hashed is large, and the digital signing platform lacks hardware support for SHAKE128 and SHAKE256, pre-hashed variants of ML-DSA might be used to reduce computational overheads. In such cases, pre-hashed variants of ML-DSA take as their input a hash of the message as computed by an alternative, and less computationally expensive, hashing algorithm. In such cases, care must be taken to ensure that an appropriate alternative hashing algorithm is being used, such as a SHA-2 hashing algorithm. In such cases, the hash used must be twice as long as the desired effective security strength. In practice, this requires the use of at least SHA-384 for the pre-hashed variant of ML-DSA-65 and at the use of at least SHA-512 for the pre-hashed variant of ML-DSA-87.

Control: ISM-1991; Revision: 0; Updated: Dec-24; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
When using ML-DSA for digital signatures, ML-DSA-65 or ML-DSA-87 is used, preferably ML-DSA-87.

Control: ISM-1992; Revision: 0; Updated: Dec-24; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
When using ML-DSA for digital signatures, the hedged variant is used whenever possible.

Control: ISM-1993; Revision: 0; Updated: Dec-24; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
Pre-hashed variants of ML-DSA-65 and ML-DSA-87 are only used when the performance of default variants is unacceptable.

Control: ISM-1994; Revision: 0; Updated: Dec-24; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
When the pre-hashed variants of ML-DSA-65 and ML-DSA-87 are used, at least SHA-384 and SHA-512 respectively are used for pre-hashing.

Using the Module-Lattice-Based Key Encapsulation Mechanism

The effective security strength of ML-KEM has a complex dependency on numerous parameters with different effective security strengths targeted by different standardised parameter sets. The ML-KEM standard contains three different parameter sets: ML-KEM-512, ML-KEM-768 and ML-KEM-1024. The use of ML-KEM-768 and ML-KEM-1024 are approved for use. However, taking into account projected technological advances in quantum computing, ML-KEM-768 will not be approved for use beyond 2030.

Control: ISM-1995; Revision: 0; Updated: Dec-24; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
When using ML-KEM for encapsulating encryption session keys (and similar keys), ML-KEM-768 or ML-KEM-1024 is used, preferably ML-KEM-1024.

Using Rivest-Shamir-Adleman

A modulus of 2048 bits for correctly implemented RSA provides 112 bits of effective security strength, with larger modulus sizes providing more bits of effective security strength. However, taking into account projected technological advances in quantum computing, RSA will not be approved for use beyond 2030.

Control: ISM-0476; Revision: 8; Updated: Dec-24; Applicability: NC, OS, P; Essential Eight: N/A
When using RSA for digital signatures, and transporting encryption session keys (and similar keys), a modulus of at least 2048 bits is used, preferably 3072 bits.

Control: ISM-1765; Revision: 1; Updated: Dec-24; Applicability: S, TS; Essential Eight: N/A
When using RSA for digital signatures, and transporting encryption session keys (and similar keys), a modulus of at least 3072 bits is used, preferably 3072 bits.

Control: ISM-0477; Revision: 9; Updated: Dec-24; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
When using RSA for digital signatures, and for transporting encryption session keys (and similar keys), a different key pair is used for digital signatures and transporting encryption session keys.

Using Secure Hashing Algorithms

For most purposes, a hashing algorithm with an output size of 224 bits provides 112 bits of effective security strength, with larger output sizes providing more bits of effective security strength. However, taking into account projected technological advances in quantum computing, SHA-224 and SHA-256 will not be approved for use beyond 2030.

Only SHA-2 hashing algorithms are approved for general purpose use. SHA-3 and XOF approval (i.e. SHA3-256, SHA3-512, SHAKE128 and SHAKE256) is restricted to use within internal steps of ML-DSA and ML-KEM.

Control: ISM-1766; Revision: 1; Updated: Dec-24; Applicability: NC, OS, P; Essential Eight: N/A
When using SHA-2 for hashing, an output size of at least 224 bits is used, preferably SHA-384 or SHA-512.

Control: ISM-1767; Revision: 1; Updated: Dec-24; Applicability: S; Essential Eight: N/A
When using SHA-2 for hashing, an output size of at least 256 bits is used, preferably SHA-384 or SHA-512.

Control: ISM-1768; Revision: 1; Updated: Dec-24; Applicability: TS; Essential Eight: N/A
When using SHA-2 for hashing, an output size of at least 384 bits is used, preferably SHA-384 or SHA-512.

Using symmetric cryptographic algorithms

When using AES, a key size of 128 bits provides 112 bits of effective security strength, with larger key sizes providing more bits of effective security strength. However, taking into account projected technological advances in quantum computing, AES-128 and AES-192 will not be approved for use beyond 2030.

The use of Electronic Codebook Mode with block ciphers allows repeated patterns in plaintext to appear as repeated patterns in ciphertext. Most plaintext, including written language and formatted files, contains significant repeated patterns. As such, malicious actors can use this to deduce possible meanings of ciphertext. The use of other modes, such as Cipher Block Chaining, Cipher Feedback, Galois/Counter Mode or Output Feedback, can prevent such attacks, although each has different properties which can make them inappropriate for certain use cases. AES is the only approved symmetric cryptographic algorithm.

Control: ISM-1769; Revision: 1; Updated: Dec-24; Applicability: NC, OS, P, S; Essential Eight: N/A
When using AES for encryption, AES-128, AES-192 or AES-256 is used, preferably AES-256.

Control: ISM-1770; Revision: 0; Updated: Mar-22; Applicability: TS; Essential Eight: N/A
When using AES for encryption, AES-192 or AES-256 is used, preferably AES-256.

Control: ISM-0479; Revision: 5; Updated: Dec-21; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
Symmetric cryptographic algorithms are not used in Electronic Codebook Mode.

Transitioning to post-quantum cryptography

The consensus model for quantum computing allows for different types of quantum attacks against traditional cryptography. While the direct impact of these quantum attacks varies across different cryptographic algorithms, there is a stark difference in impact between asymmetric cryptographic algorithms and symmetric cryptographic algorithms.

One known quantum attack (using Shor's algorithm) effectively defeats all traditional cryptography that relies upon asymmetric cryptographic algorithms such as DH, ECDH, ECDSA or RSA. The efficiency of this is such that it is infeasible to securely use these AACAs in the presence of a cryptographically relevant quantum computer (CRQC). While a CRQC does not currently exist, the trajectory of technological advances in quantum computing means that these AACAs will need to be phased out in favour of alternative AACAs that offer greater protection. As such, the development or procurement of new cryptographic equipment and software, which is intended to be used beyond 2030, should be undertaken with the goal of supporting ASD-approved post-quantum cryptographic algorithms by 2030.

The impact of quantum attacks on hashing algorithms and symmetric cryptographic algorithms, such as SHA-2 and AES, is unlikely to be felt for some time. However, for interoperability reasons, the design and provision of new cryptographic equipment and software, which is intended to be used beyond 2030, should support SHA-384, SHA-512 and AES-256.

Control: ISM-1917; Revision: 1; Updated: Dec-24; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
The development and procurement of new cryptographic equipment and software ensures support for the use of ML-DSA-87, ML-KEM-1024, SHA-384, SHA-512 and AES-256 by no later than 2030.

Post-quantum traditional hybrid schemes

A post-quantum traditional hybrid scheme is a multi-algorithm scheme where at least one cryptographic algorithm is a post-quantum cryptographic algorithm (e.g. ML-KEM) and at least one cryptographic algorithm is a traditional cryptographic algorithm (e.g. RSA). Generally, such schemes have the advantage of the security offered by the traditional cryptographic algorithm in the event that the post-quantum cryptographic algorithm is vulnerable to an implementation flaw or new attack. This advantage comes at the cost of increased complexity, making maintenance, analysis and secure implementation more difficult, as well as having greater computational and bandwidth overheads.

The use of post-quantum traditional hybrid schemes is not recommended, however, it is not prohibited. If such schemes are to be used, at least one of the post-quantum or traditional cryptographic algorithms, or both, must be an AACA. It is important to note though, that in the presence of a CRQC, the security of such schemes are reduced to that provided by the post-quantum cryptographic algorithm. As such, there is no practical value in the use of such schemes in the presence of a CRQC. An organisation choosing to implement a post-quantum traditional hybrid scheme should also keep in mind the eventual additional cost of transitioning to a pure post-quantum scheme in the future.

Control: ISM-1996; Revision: 0; Updated: Dec-24; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
When a post-quantum traditional hybrid scheme is used, either the post-quantum cryptographic algorithm, the traditional cryptographic algorithm or both are AACAs.

Further information

Further information on the United States’ Commercial National Security Algorithm Suite is available from the United States’ National Security Agency.

Further information on post-quantum traditional hybrid schemes can be found in the United Kingdom’s National Cyber Security Centre’s Next steps in preparing for post-quantum cryptography guidance.

Further information on how to combine the different components of a post-quantum traditional hybrid scheme used for key encapsulation can be found in NIST SP 800-56C Rev. 2, Recommendation for Key-Derivation Methods in Key-Establishment Schemes. Note, this publication does not pertain to post-quantum traditional hybrid schemes used for digital signatures.

Further information on planning for the transition to post-quantum cryptography can be found in ASD’s Planning for Post-Quantum Cryptography publication.

ASD-Approved Cryptographic Protocols

High assurance cryptographic protocols

High assurance cryptographic protocols, which are not covered in this section, can be used for the protection of SECRET and TOP SECRET data if they are suitably implemented in HACE. Further information on high assurance cryptographic protocols can be obtained from ASD.

ASD-Approved Cryptographic Protocols

There is no guarantee of a protocol’s resistance to currently unknown attacks. However, the protocols listed in this section have been extensively scrutinised by industry and academic communities in a practical and theoretical setting. Approval for the use of the protocols listed in this section is limited to cases where they are implemented in accordance with these guidelines.

The AACPs are:

• Transport Layer Security (TLS)
• Secure Shell (SSH)
• Secure/Multipurpose Internet Mail Extension (S/MIME)
• OpenPGP Message Format
• Internet Protocol Security (IPsec)
• Wi-Fi Protected Access 2
• Wi-Fi Protected Access 3.

Using ASD-Approved Cryptographic Protocols

If cryptographic equipment or software implements unapproved protocols, it is possible that these protocols could be used without a user’s knowledge. In combination with an assumed level of security confidence, this can represent a security risk. As such, an organisation can ensure that only AACPs or high assurance cryptographic protocols can be used by disabling unapproved protocols (preferred) or by advising users not to use unapproved protocols via usage policies.

Control: ISM-0481; Revision: 6; Updated: Dec-21; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
Only AACPs or high assurance cryptographic protocols are used by cryptographic equipment and software.

Further information

Further information on AACPs can be found in the following sections of these guidelines.

Further information on the use of Wi-Fi Protected Access 2 and Wi-Fi Protected Access 3 can be found in the wireless networks section of the Guidelines for Networking.

Transport Layer Security

Using Transport Layer Security

When using IT equipment or software that implements TLS, controls for using AACAs and AACPs in the ASD-Approved Cryptographic Algorithms and ASD-Approved Cryptographic Protocols sections of these guidelines will also need to be consulted.

Configuring Transport Layer Security

The terms Secure Sockets Layer and TLS have traditionally been used interchangeably. However, Secure Sockets Layer and TLS version 1.2 and earlier are no longer considered suitable for use as an AACP. As such, an organisation implementing TLS should use only the latest version of TLS (i.e. TLS version 1.3). In addition, a number of security risks exist when TLS is configured in an insecure manner. To mitigate these security risks, TLS clients and servers should be configured to enforce secure settings at the time of the TLS handshake. In situations where this is not possible, such as for some multi-tenancy environments (e.g. content delivery networks), additional controls will need to be implemented. For example, by further restricting the permitted TLS configuration within Layer 7 authorisation logic.

Control: ISM-1139; Revision: 6; Updated: Mar-22; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
Only the latest version of TLS is used for TLS connections.

Control: ISM-1369; Revision: 3; Updated: Mar-22; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
AES-GCM is used for encryption of TLS connections.

Control: ISM-1370; Revision: 3; Updated: Mar-22; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
Only server-initiated secure renegotiation is used for TLS connections.

Control: ISM-1372; Revision: 3; Updated: Mar-22; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
DH or ECDH is used for key establishment of TLS connections.

Control: ISM-1448; Revision: 2; Updated: Mar-22; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
When using DH or ECDH for key establishment of TLS connections, the ephemeral variant is used.

Control: ISM-1373; Revision: 2; Updated: Mar-22; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
Anonymous DH is not used for TLS connections.

Control: ISM-1374; Revision: 3; Updated: Mar-22; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
SHA-2-based certificates are used for TLS connections.

Control: ISM-1375; Revision: 4; Updated: Mar-22; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
SHA-2 is used for the Hash-based Message Authentication Code (HMAC) and pseudorandom function (PRF) for TLS connections.

Control: ISM-1553; Revision: 1; Updated: Mar-22; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
TLS compression is disabled for TLS connections.

Control: ISM-1453; Revision: 1; Updated: Sep-18; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
Perfect Forward Secrecy (PFS) is used for TLS connections.

Further information

Further information on implementing TLS can be found in ASD’s Implementing Certificates, TLS, HTTPS and Opportunistic TLS publication.

Further information on TLS filtering in gateways can be found in the web content filters section of the Guidelines for Gateways.

Secure Shell

Using Secure Shell

When using IT equipment or software that implements SSH, controls for using AACAs and AACPs in the ASD-Approved Cryptographic Algorithms and ASD-Approved Cryptographic Protocols sections of these guidelines will also need to be consulted.

Configuring Secure Shell

SSH version 1 was found to have a number of vulnerabilities and was subsequently replaced by SSH version 2. As such, an organisation implementing SSH should disable the use of SSH version 1. In addition, a number of security risks exist when SSH is configured in an insecure manner. To mitigate these security risks, SSH should be configured as per the settings below.

The settings below are based on OpenSSH. An organisation using other implementations of SSH should adapt these settings to suit their SSH implementation.

Control: ISM-1506; Revision: 1; Updated: Mar-22; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
The use of SSH version 1 is disabled for SSH connections.

Control: ISM-0484; Revision: 6; Updated: Dec-21; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
The SSH daemon is configured to:

• only listen on the required interfaces (ListenAddress xxx.xxx.xxx.xxx)
• have a suitable login banner (Banner x)
• have a login authentication timeout of no more than 60 seconds (LoginGraceTime 60)
• disable host-based authentication (HostbasedAuthentication no)
• disable rhosts-based authentication (IgnoreRhosts yes)
• disable the ability to login directly as root (PermitRootLogin no)
• disable empty passwords (PermitEmptyPasswords no)
• disable connection forwarding (AllowTCPForwarding no)
• disable gateway ports (GatewayPorts no)
• disable X11 forwarding (X11Forwarding no).

Authentication mechanisms

As public key-based authentication schemes offer stronger authentication than passphrase-based authentication schemes, due to being much less susceptible to brute-force attacks, they should be used for SSH connections. Furthermore, in order to protect SSH private keys, access to such keys should be protected via the use of passphrases or key encryption keys.

Control: ISM-0485; Revision: 3; Updated: Sep-18; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
Public key-based authentication is used for SSH connections.

Control: ISM-1449; Revision: 1; Updated: Sep-18; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
SSH private keys are protected with a passphrase or a key encryption key.

Automated remote access

If using logins without a passphrase for automated purposes, a number of security risks may arise, specifically:

• if access from unknown Internet Protocol (IP) addresses is not restricted, malicious actors could automatically authenticate to systems without needing to know any passphrases
• if port forwarding is not disabled, or it is not configured securely, access may be gained to forwarded ports, thereby, creating a communication channel between malicious actors and a host
• if agent credential forwarding is enabled, malicious actors could connect to the stored authentication credentials and use them to connect to other trusted hosts, or even intranet hosts if port forwarding has been allowed as well
• if X11 forwarding is not disabled, malicious actors could gain control of displays as well as keyboard and mouse control functions
• if console access is allowed, every user who logs into the console could run programs that are normally restricted to authenticated users.

To assist in mitigating these security risks, it is essential that the ‘forced command’ option is used to specify what command is executed and parameter checking is enabled.

Control: ISM-0487; Revision: 5; Updated: Sep-24; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
When using logins without a passphrase for SSH connections, the following are disabled:

• access from IP addresses that do not require access
• port forwarding
• agent credential forwarding
• X11 forwarding
• console access.

Control: ISM-0488; Revision: 4; Updated: Mar-22; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
If using remote access without the use of a passphrase for SSH connections, the ‘forced command’ option is used to specify what command is executed and parameter checking is enabled.

SSH-agent

SSH-agent and similar key caching programs manage private keys stored on workstations and servers. Specifically, when an SSH-agent launches, it requests a user’s passphrase to unlock the user’s private key. Subsequent access to remote systems is then performed by the SSH-agent and does not require the user to re-enter their passphrase. Screen locks and expiring key caches can be used to ensure that a user’s private key is not left unlocked for a long period of time.

Control: ISM-0489; Revision: 5; Updated: Mar-22; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
When SSH-agent or similar key caching programs are used, it is limited to workstations and servers with screen locks and key caches that are set to expire within four hours of inactivity.

Further information

Further information on configuring OpenSSH is available from the OpenSSH project.

Secure/Multipurpose Internet Mail Extension

Using Secure/Multipurpose Internet Mail Extension

When using IT equipment or software that implements S/MIME, controls for using AACAs and AACPs in the ASD-Approved Cryptographic Algorithms and ASD-Approved Cryptographic Protocols sections of these guidelines will also need to be consulted.

Configuring Secure/Multipurpose Internet Mail Extension

S/MIME version 2.0 required the use of weaker cryptography than approved for use in these guidelines. As such, S/MIME version 3.0 was the first version to be approved for use as an AACP.

Control: ISM-0490; Revision: 4; Updated: Mar-22; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
Versions of S/MIME earlier than S/MIME version 3.0 are not used for S/MIME connections.

Internet Protocol Security

Using Internet Protocol Security

When using IT equipment or software that implements IPsec, controls for using AACAs and AACPs in the ASD-Approved Cryptographic Algorithms and ASD-Approved Cryptographic Protocols sections of these guidelines will also need to be consulted.

Mode of operation

IPsec can be operated in tunnel mode or transport mode. The tunnel mode of operation is preferred as it provides full encapsulation of IP packets while the transport mode of operation only encapsulates the payload of IP packets.

Control: ISM-0494; Revision: 3; Updated: Sep-18; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
Tunnel mode is used for IPsec connections; however, if using transport mode, an IP tunnel is used.

Protocol selection

IPsec contains two major protocols, the Authentication Header (AH) protocol and the Encapsulating Security Payload (ESP) protocol. In order to provide a secure Virtual Private Network style connection, authentication and encryption are needed. While the AH and ESP protocols can provide authentication, for the IP packet and the payload respectively, only the ESP protocol can provide encryption.

As the combined use of the AH protocol and the ESP protocol is not supported by Internet Key Exchange (IKE) version 2, the ESP protocol should be used for authentication and encryption of IPsec connections.

Control: ISM-0496; Revision: 5; Updated: Mar-22; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
The ESP protocol is used for authentication and encryption of IPsec connections.

Key exchange

There are several methods for establishing shared keying material for IPsec connections, including manual keying and the IKE protocol. As the IKE protocol addresses a number of security risks associated with manual keying, it is the preferred method for key establishment. Note, as IKE version 1 has been deprecated, IKE version 2 should be used.

Control: ISM-1233; Revision: 2; Updated: Mar-22; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
IKE version 2 is used for key exchange when establishing IPsec connections.

Encryption algorithms

The only approved encryption algorithm for IPsec connections is AES. IKE version 2 supports the use of AES with Cipher Block Chaining, Counter Mode, Counter with Cipher Block Chaining Message Authentication Code, and Galois/Counter Mode. Note, however, supported modes may vary between different cryptographic equipment and software.

Control: ISM-1771; Revision: 0; Updated: Mar-22; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
AES is used for encrypting IPsec connections, preferably ENCR_AES_GCM_16.

Pseudorandom function

IKE version 2 requires the use of a PRF in order to generate random data for cryptographic operations. The approved hashing algorithms that can be used for the PRF are HMAC-SHA256, HMAC-SHA384 and HMAC-SHA512. Note, taking into account projected technological advances in quantum computing, HMAC-SHA256 will not be approved for use beyond 2030.

Control: ISM-1772; Revision: 0; Updated: Mar-22; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
PRF_HMAC_SHA2_256, PRF_HMAC_SHA2_384 or PRF_HMAC_SHA2_512 is used for IPsec connections, preferably PRF_HMAC_SHA2_512.

Integrity algorithms

The approved integrity algorithms for IPsec connections are HMAC-SHA256, HMAC-SHA384 and HMAC-SHA512. However, if using AES with Galois/Counter Mode as the encryption algorithm, it can also be used for authentication purposes. In such cases, the integrity algorithm should be configured as NONE. Note, taking into account projected technological advances in quantum computing, HMAC-SHA256 will not be approved for use beyond 2030.

Control: ISM-0998; Revision: 5; Updated: Mar-22; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
AUTH_HMAC_SHA2_256_128, AUTH_HMAC_SHA2_384_192, AUTH_HMAC_SHA2_512_256 or NONE (only with AES-GCM) is used for authenticating IPsec connections, preferably NONE.

Diffie-Hellman groups

A sufficiently large DH modulus provides greater security for key exchanges when establishing IPsec connections. Note, taking into account projected technological advances in quantum computing, DH and ECDH will not be approved for use beyond 2030.

Control: ISM-0999; Revision: 6; Updated: Mar-22; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
DH or ECDH is used for key establishment of IPsec connections, preferably 384-bit random ECP group, 3072-bit MODP Group or 4096-bit MODP Group.

Security association lifetimes

Using a security association lifetime of less than four hours (14400 seconds) can provide a balance between security and usability.

Control: ISM-0498; Revision: 4; Updated: Mar-22; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
A security association lifetime of less than four hours (14400 seconds) is used for IPsec connections.

Perfect Forward Secrecy

Using PFS reduces the impact of the compromise of a security association.

Control: ISM-1000; Revision: 4; Updated: Sep-18; Applicability: NC, OS, P, S, TS; Essential Eight: N/A
PFS is used for IPsec connections.