commit 3c34000c9c28b6a55e2c4333a5ad0ccf99bd4026 Author: Taylor R Campbell <campbell+tor@mumble.net> Date: Fri Oct 19 17:43:17 2018 +0000 Specify the ED25519-V3 private key format, and explain why it is so. --- control-spec.txt | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/control-spec.txt b/control-spec.txt index 6f0a543..6a04b65 100644 --- a/control-spec.txt +++ b/control-spec.txt @@ -1671,8 +1671,18 @@ (The KeyBlob format is left intentionally opaque, however for "RSA1024" keys it is currently the Base64 encoded DER representation of a PKCS#1 - RSAPrivateKey, with all newlines removed. For a "ED25519-V3" key is a Base64 - encoded ed25519 private key.) + RSAPrivateKey, with all newlines removed. For a "ED25519-V3" key is + the Base64 encoding of the concatenation of the 32-byte ed25519 secret + scalar in little-endian and the 32-byte ed25519 PRF secret.) + + [Note: The ED25519-V3 format is not the same as, e.g., SUPERCOP + ed25519/ref, which stores the concatenation of the 32-byte ed25519 + hash seed concatenated with the 32-byte public key, and which derives + the secret scalar and PRF secret by expanding the hash seed with + SHA-512. Our key blinding scheme is incompatible with storing + private keys as seeds, so we store the secret scalar alongside the + PRF secret, and just pay the cost of recomputing the public key when + importing an ED25519-V3 key.] (The "NEW:BEST" option obeys the HiddenServiceVersion torrc option default value. Currently it is 2.)