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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.

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2 回答 2

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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

于 2020-06-28T08:22:44.387 回答
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Ed25519键可以X25519很容易地转换为键，使用的扭曲爱德华兹曲线Ed25519和使用的蒙哥马利曲线X25519是birationally等效的。

爱德华兹曲线上的点通常称为 ( x, y)，而蒙哥马利曲线上的点通常称为 ( u, v)。

您不需要库来进行转换，它真的很简单......

(u, v) = ((1+y)/(1-y), sqrt(-486664)*u/x)
(x, y) = (sqrt(-486664)*u/v, (u-1)/(u+1))

这是Google 的 Golang 安全主管 Filippo Valsorda 撰写的一篇很棒的博客，讨论了这个话题。

于 2020-06-26T15:07:49.467 回答