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MLA key file format

MLA can use cryptography for signature and/or encryption. Thus it needs to operate with keys. An implementation can get access to these keys from a serialized format described here.

The string || denotes concatenation.

Private key file format

A private key file is an ASCII file, which may use mlapriv as file extension. The file (or whatever serialization medium) content is PrivFormatHeader||<CR><LF>PrivEncHdr||B64Priv4Enc||<CR><LF>||PrivSigHdr||B64Priv4Sig||<CR><LF>||B64PrivOpts||<CR><LF>||PrivFormatFooter||<CR><LF> where <CR> is ASCII carriage return, <LF> is ASCII line feed, and PrivFormatHeader, PrivEncHdr, B64Priv4Enc, PrivSigHdr, B64Priv4Sig, B64PrivOpts and PrivFormatFooter are described below.

  • PrivFormatHeader is the ASCII string DO NOT SEND THIS TO ANYONE - MLA PRIVATE KEY FILE V1.

  • PrivEncHdr is the ASCII string MLA PRIVATE DECRYPTION KEY (note the trailing space).

  • PrivSigHdr is the ASCII string MLA PRIVATE SIGNING KEY (note the trailing space).

  • B64Priv4Enc is the base64 encoding (RFC 4648) of EncMethodId||PrivEncOpts||X25519PrivKey||MLKEM1024PrivKey where EncMethodId, PrivEncOpts, X25519PrivKey and MLKEM1024PrivKey are described below.

  • B64Priv4Sig is the base64 encoding of SigMethodId||PrivSigOpts||Ed25519PrivKey||MLDSA87PrivKey where MethodId, PrivEncOpts, Ed25519PrivKey and MLDSA87PrivKey are described below.

  • PrivFormatFooter is the ASCII string END OF MLA PRIVATE KEY FILE

  • The only valid EncMethodId for the moment is the ASCII mla-kem-private-x25519-mlkem1024.

  • The only valid SigMethodId for the moment is the ASCII mla-signature-private-ed25519-mldsa87.

  • X25519PrivKey is a X25519 private key as specified in RFC 7748.

  • MLKEM1024PrivKey is an ML-KEM-1024 private key seed (d,z) as specified in FIPS 203 algorithm 16. d and z are concatenated in this order.

  • Ed25519PrivKey is a Ed25519 private key as specified in RFC 8032.

  • MLDSA87PrivKey is an ML-DSA-87 private key seed xi as specified in FIPS 204 algorithm 6.

For PrivEncOpts and PrivSigOpts, refer to below generic explanation for KeyOpts.

  • B64PrivOpts is a base64 encoded KeyOpts.

Public key file format

A public key file is an ASCII file, which may use mlapub as file extension. The file (or whatever serialization medium) content is PubFormatHeader||<CR><LF>||PubEncHdr||B64Pub4Enc||<CR><LF>||PubSigHdr||B64Pub4Sig||<CR><LF>||B64PubOpts||<CR><LF>||PubFormatFooter||<CR><LF> where <CR> is ASCII carriage return, <LF> is ASCII line feed, and PubFormatHeader, PubEncHdr, B64Pub4Enc, PubSigHdr, B64Pub4Sig, B64PubOpts and PubFormatFooter are described below.

  • PubFormatHeader is the ASCII string MLA PUBLIC KEY FILE V1.

  • PubEncHdr is the ASCII string `MLA PUBLIC ENCRYPTION KEY " (note the trailing space).

  • PubSigHdr is the ASCII string `MLA PUBLIC SIGNATURE VERIFICATION KEY " (note the trailing space).

  • B64Pub4Enc is the base64 encoding (RFC 4648) of EncMethodId||PubEncOpts||X25519PubKey||MLKEM1024PubKey where EncMethodId, PubEncOpts, X25519PubKey and MLKEM1024PubKey are described below.

  • B64Pub4Sig is the base64 encoding of SigMethodId||PubSigOpts||Ed25519PubKey||MLDSA87PubKey where MethodId, PubEncOpts, Ed25519PubKey and MLDSA87PubKey are described below.

  • PubFormatFooter is the ASCII string END OF MLA PUBLIC KEY FILE

  • The only valid EncMethodId for the moment is the ASCII mla-kem-public-x25519-mlkem1024.

  • The only valid SigMethodId for the moment is the ASCII mla-signature-verification-public-ed25519-mldsa87.

  • X25519PubKey is a X25519 public key as specified in RFC 7748.

  • MLKEM1024PubKey is an ML-KEM-1024 public key as specified in FIPS 203.

  • Ed25519PubKey is a Ed25519 public key as specified in RFC 8032.

  • MLDSA87PubKey is an ML-DSA-87 public key as specified in FIPS 204.

For PubEncOpts and PubSigOpts, refer to below generic explanation for KeyOpts.

  • B64PubOpts is a base64 encoded KeyOpts.

Options

KeyOpts fields are options fields for future-proofing the format in case of later non-breaking optional additions to the key file format. It is a length-value field where length is the length in bytes of value, serialized as a 4 bytes little-endian integer. Possible values are left unspecified for the moment, but implementations, particularly for public keys, should read length bytes correctly in case some options are specified later.