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Zero XOR CTR IV in ECIES and remove it from ciphertext

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This commit is contained in:
Gustav Simonsson 2015-05-01 08:07:22 +02:00
parent 3fef601903
commit d1f39f841b
1 changed files with 15 additions and 12 deletions
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27
crypto/ecies/ecies.go
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@ -1,6 +1,7 @@
package ecies
import (
"bytes"
"crypto/cipher"
"crypto/ecdsa"
"crypto/elliptic"
@ -185,16 +186,17 @@ func symEncrypt(rand io.Reader, params *ECIESParams, key, m []byte) (ct []byte,
if err != nil {
return
}
iv, err := generateIV(params, rand)
if err != nil {
return
}
/*
In SEC 1 Version 2.0 the IV value is not specified in for XOR CTR.
It is specified, however, that it should not be transmitted as part of the ciphertext.
This means it cannot be random, as the other party would not know the value.
Therefore we set it to the zeroed value defined for AES in CTR mode.
*/
iv := bytes.Repeat([]byte{0}, 16)
ctr := cipher.NewCTR(c, iv)
ct = make([]byte, len(m)+params.BlockSize)
copy(ct, iv)
ctr.XORKeyStream(ct[params.BlockSize:], m)
ct = make([]byte, len(m))
ctr.XORKeyStream(ct, m)
return
}
@ -206,10 +208,11 @@ func symDecrypt(rand io.Reader, params *ECIESParams, key, ct []byte) (m []byte,
return
}
ctr := cipher.NewCTR(c, ct[:params.BlockSize])
iv := bytes.Repeat([]byte{0}, 16)
ctr := cipher.NewCTR(c, iv)
m = make([]byte, len(ct)-params.BlockSize)
ctr.XORKeyStream(m, ct[params.BlockSize:])
m = make([]byte, len(ct))
ctr.XORKeyStream(m, ct)
return
}
@ -245,7 +248,7 @@ func Encrypt(rand io.Reader, pub *PublicKey, m, s1, s2 []byte) (ct []byte, err e
hash.Reset()
em, err := symEncrypt(rand, params, Ke, m)
if err != nil || len(em) <= params.BlockSize {
if err != nil {
return
}