Introduction

Libreswan currently supports RSA as Digital Signature Authentication method, so it needs to be extended internally to use other methods, such as ECDSA or EDDSA. Implementation of ECC/ECDSA requires the modification of the existing Libreswan public key code to fix the RSA only parts so that it is able to accept different new types of keys in the future ( not just limited to EDDSA ). Libreswan will then be compliant to RFC-7427 and RFC-8247.

Use Cases

Use Case 1: As an admin I should be able to configure ecdsa in libreswan ipsec.conf as a digital signature authentication method

• Requirement 1: As per RFC 8247, ecdsa with sha2-256 should be supported and ecdsa with sha1 must not be supported.
• Requirement 2: Digital signature recommendations for hash function specify that sha2-256 must, sha2-384 may and sha2-512 should be supported. ( Should Libreswan support all three variants? )
• Requirement 3: Support for authby=secret|rsasig|null|never|rsa-HASH|ecdsa-HASH in the ipsec.conf

Use Case 2: As an admin I should be able to configure other public key algorithms along with ecdsa. Rational : Ecdsa might not be implemented in all peers.

• Requirement 4: authby = ecdsa-HASH|rsa-HASH. RSA can be configured to act as fallback incase Digital signature authentication with ecdsa fails.
• Requirement 5: if authby = ecdsa-HASH and there is no fallback then if the peer does not support ecdsa, IKE Authentication fails (Default behaviour, Retry?)

Use Case 3: As an Initiator, I should initiate IKE AUTH messages with ecdsa support.

• Requirement 6: Authentication data must have the ASN.1 Algorithm identifiers as specified in Section A.3 of RFC 7427
• Requirement 7: Certificate Request payloads must have the algorithmIdentifier set to sha2WithECDSAEncryption
• Requirement 8: ECDSA Signature should be sent out in Authentication payload

Use Case 4: As a responder, I should respond to IKE AUTH messages with ecdsa support.

• Requirement 9: Authentication data received must have the ASN.1 Algorithm identifiers as specified in Section A.3 of RFC 7427
• Requirement 10: Certificate Request payloads with algorithmIdentifier set to sha2WithECDSAEncryption must be validated.
• Requirement 11: If ECDSA Signature verification fails, IKE AUTH failure is sent.

Use Case 5: Interoperability with Strongswan, Apple and ELVIS-PLUS