Blind signatures

WIP

Blind signatures use the following primitives which need to be saved into a file system or transferred over the network:

BigNum (32B): since the curve is secp256k1, the bignums are 256bits long (32 bytes). They are serialized using OpenSSL's BN_bn2binpad

Eliptic curve points (33B): again, since we're using secp256k1, the coordinates X and Y are 32 bytes. We use compressed format compatible with OpenSSL's EC_POINT_set_compressed_coordinates. I tried to replicate how it's stored in other places and how OpenSSL behaves, so the data should be loadable by other software just like a bitcoin private key

the first byte is 0x02 or 0x03 (which determines which of the two Y coordinates it uses, the difference is that one is even and one is odd. Other bits are ignored by Bitmessage
the next 32 bytes are the X coordinate (which is a bignum)

Private key (32B): private key is a 256 bit bignum

Public key (35B): public key is two bytes of parameters followed by an EC Point as described above

first byte is expiration, split into two 4-bit parts. The lower 4 bits are month (0 - 11), and the higher 4 bits are year (add 2020 to get the actual year). For example 0x03 is April 2020.
second byte is value (1-255)
the rest of the bytes (33B) is an EC point

Random integer provided by the signer to the requester during signing (33B): is an EC point

Blinded signature(32B): Blinded signature is a 256bit bignum

Unblinded Signature (65B): is a bignum (32B) followed by an EC point (33B)

Signature chain (100 bytes per level):

Begins with the CA pubkey (35 bytes)
on the next levels the intermediary pubkey (35B) and a signature of that pubkey signed by the parent pubkey (65B)
and on the last level, the signature of the message signed by the parent pubkey (65B)

to the other wiki at sourceforge