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algorithm - How do I sign a curve25519 key in golang?

问题描述

I am trying to implement the X3DH algorithm from Signal in Go. However, I got stuck on how to sign the Public Signed PreKey.

Per the specifications it is supposed to be an X25519 key. In looking at previous implementations on Github they generated a [32]byte key from the curve25519 package and then converted it to an ed25519 key and then signed it.

However, the packages they used for the conversion are deprecated (github.com/agl/ed25519). Therefore, I either need to be able to convert the keys to ed25519 so I can sign them with the current ed25519 package (golang.org/x/crypto/25519) or implement a sign and verify function for curve25519 keys.

标签： algorithmgocryptographyed25519curve-25519

解决方案

这需要一个公共的curve25519 密钥并将其转换为一个ed25519 的公共密钥。我没有编写此代码，但似乎正在做上面伍德斯托克所说的事情。欢迎提供更多信息：

func Verify(publicKey [32]byte, message []byte, signature *[64]byte) bool {

publicKey[31] &= 0x7F

/* Convert the Curve25519 public key into an Ed25519 public key.  In
particular, convert Curve25519's "montgomery" x-coordinate into an
Ed25519 "edwards" y-coordinate:
ed_y = (mont_x - 1) / (mont_x + 1)
NOTE: mont_x=-1 is converted to ed_y=0 since fe_invert is mod-exp
Then move the sign bit into the pubkey from the signature.
*/

var edY, one, montX, montXMinusOne, montXPlusOne FieldElement
FeFromBytes(&montX, &publicKey)
FeOne(&one)
FeSub(&montXMinusOne, &montX, &one)
FeAdd(&montXPlusOne, &montX, &one)
FeInvert(&montXPlusOne, &montXPlusOne)
FeMul(&edY, &montXMinusOne, &montXPlusOne)

var A_ed [32]byte
FeToBytes(&A_ed, &edY)

A_ed[31] |= signature[63] & 0x80
signature[63] &= 0x7F

var sig = make([]byte, 64)
var aed = make([]byte, 32)

copy(sig, signature[:])
copy(aed, A_ed[:])

return ed25519.Verify(aed, message, sig)

这使用“golang.org/x/crypto/ed25519/internal”中的函数

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