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crypto/rsa: left-pad PKCS#1 v1.5 outputs.

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OpenSSL requires that RSA signatures be exactly the same byte-length
as the modulus. Currently it'll reject ~1/256 of our signatures: those
that end up a byte shorter.

Fixes #3796.

R=golang-dev, edsrzf, r
CC=golang-dev
https://golang.org/cl/6352093
This commit is contained in:
Adam Langley 2012-07-11 12:47:12 -04:00
parent 82cbcb0dd5
commit 93ea79ee7e
1 changed files with 22 additions and 7 deletions
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29
src/pkg/crypto/rsa/pkcs1v15.go
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@ -25,10 +25,10 @@ func EncryptPKCS1v15(rand io.Reader, pub *PublicKey, msg []byte) (out []byte, er
return
}
// EM = 0x02 || PS || 0x00 || M
em := make([]byte, k-1)
em[0] = 2
ps, mm := em[1:len(em)-len(msg)-1], em[len(em)-len(msg):]
// EM = 0x00 || 0x02 || PS || 0x00 || M
em := make([]byte, k)
em[1] = 2
ps, mm := em[2:len(em)-len(msg)-1], em[len(em)-len(msg):]
err = nonZeroRandomBytes(ps, rand)
if err != nil {
return
@ -38,7 +38,9 @@ func EncryptPKCS1v15(rand io.Reader, pub *PublicKey, msg []byte) (out []byte, er
m := new(big.Int).SetBytes(em)
c := encrypt(new(big.Int), pub, m)
out = c.Bytes()
copyWithLeftPad(em, c.Bytes())
out = em
return
}
@ -185,9 +187,12 @@ func SignPKCS1v15(rand io.Reader, priv *PrivateKey, hash crypto.Hash, hashed []b
m := new(big.Int).SetBytes(em)
c, err := decrypt(rand, priv, m)
if err == nil {
s = c.Bytes()
if err != nil {
return
}
copyWithLeftPad(em, c.Bytes())
s = em
return
}
@ -241,3 +246,13 @@ func pkcs1v15HashInfo(hash crypto.Hash, inLen int) (hashLen int, prefix []byte,
}
return
}
// copyWithLeftPad copies src to the end of dest, padding with zero bytes as
// needed.
func copyWithLeftPad(dest, src []byte) {
numPaddingBytes := len(dest) - len(src)
for i := 0; i < numPaddingBytes; i++ {
dest[i] = 0
}
copy(dest[numPaddingBytes:], src)
}