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125 lines
3 KiB
Go
125 lines
3 KiB
Go
// Copyright 2013 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package ed25519 implements the Ed25519 signature algorithm. See
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// http://ed25519.cr.yp.to/.
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package ed25519
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// This code is a port of the public domain, "ref10" implementation of ed25519
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// from SUPERCOP.
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import (
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"crypto/sha512"
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"crypto/subtle"
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"io"
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"github.com/agl/ed25519/edwards25519"
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)
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const (
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PublicKeySize = 32
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PrivateKeySize = 64
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SignatureSize = 64
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)
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// GenerateKey generates a public/private key pair using randomness from rand.
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func GenerateKey(rand io.Reader) (publicKey *[PublicKeySize]byte, privateKey *[PrivateKeySize]byte, err error) {
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privateKey = new([64]byte)
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publicKey = new([32]byte)
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_, err = io.ReadFull(rand, privateKey[:32])
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if err != nil {
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return nil, nil, err
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}
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h := sha512.New()
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h.Write(privateKey[:32])
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digest := h.Sum(nil)
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digest[0] &= 248
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digest[31] &= 127
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digest[31] |= 64
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var A edwards25519.ExtendedGroupElement
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var hBytes [32]byte
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copy(hBytes[:], digest)
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edwards25519.GeScalarMultBase(&A, &hBytes)
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A.ToBytes(publicKey)
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copy(privateKey[32:], publicKey[:])
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return
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}
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// Sign signs the message with privateKey and returns a signature.
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func Sign(privateKey *[PrivateKeySize]byte, message []byte) *[SignatureSize]byte {
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h := sha512.New()
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h.Write(privateKey[:32])
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var digest1, messageDigest, hramDigest [64]byte
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var expandedSecretKey [32]byte
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h.Sum(digest1[:0])
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copy(expandedSecretKey[:], digest1[:])
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expandedSecretKey[0] &= 248
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expandedSecretKey[31] &= 63
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expandedSecretKey[31] |= 64
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h.Reset()
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h.Write(digest1[32:])
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h.Write(message)
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h.Sum(messageDigest[:0])
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var messageDigestReduced [32]byte
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edwards25519.ScReduce(&messageDigestReduced, &messageDigest)
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var R edwards25519.ExtendedGroupElement
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edwards25519.GeScalarMultBase(&R, &messageDigestReduced)
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var encodedR [32]byte
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R.ToBytes(&encodedR)
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h.Reset()
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h.Write(encodedR[:])
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h.Write(privateKey[32:])
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h.Write(message)
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h.Sum(hramDigest[:0])
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var hramDigestReduced [32]byte
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edwards25519.ScReduce(&hramDigestReduced, &hramDigest)
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var s [32]byte
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edwards25519.ScMulAdd(&s, &hramDigestReduced, &expandedSecretKey, &messageDigestReduced)
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signature := new([64]byte)
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copy(signature[:], encodedR[:])
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copy(signature[32:], s[:])
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return signature
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}
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// Verify returns true iff sig is a valid signature of message by publicKey.
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func Verify(publicKey *[PublicKeySize]byte, message []byte, sig *[SignatureSize]byte) bool {
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if sig[63]&224 != 0 {
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return false
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}
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var A edwards25519.ExtendedGroupElement
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if !A.FromBytes(publicKey) {
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return false
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}
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h := sha512.New()
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h.Write(sig[:32])
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h.Write(publicKey[:])
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h.Write(message)
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var digest [64]byte
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h.Sum(digest[:0])
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var hReduced [32]byte
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edwards25519.ScReduce(&hReduced, &digest)
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var R edwards25519.ProjectiveGroupElement
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var b [32]byte
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copy(b[:], sig[32:])
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edwards25519.GeDoubleScalarMultVartime(&R, &hReduced, &A, &b)
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var checkR [32]byte
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R.ToBytes(&checkR)
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return subtle.ConstantTimeCompare(sig[:32], checkR[:]) == 1
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}
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