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rsa.go
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rsa.go
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package crypto
import (
"crypto/rsa"
// #nosec
//
// Allowing sha1 because it is used in MTProto itself.
"crypto/sha1"
"math/big"
)
// RSAKeyBits is RSA key size.
//
// Can be used as rsa.GenerateKey(src, RSAKeyBits).
const RSAKeyBits = 2048
const (
rsaLen = 256
rsaWithHashLen = 255
rsaDataLen = rsaWithHashLen - sha1.Size
)
// RSAPublicDecrypt recovers the message digest from the raw signature
// using the signer’s RSA public key.
//
// See also OpenSSL’s RSA_public_decrypt with RSA_NO_PADDING.
func RSAPublicDecrypt(pub *rsa.PublicKey, sig []byte) ([]byte, error) {
k := pub.Size()
if k < 11 || k != len(sig) {
return nil, rsa.ErrVerification
}
c := new(big.Int).SetBytes(sig)
e := big.NewInt(int64(pub.E))
m := new(big.Int).Exp(c, e, pub.N)
return m.Bytes(), nil
}
func rsaEncrypt(data []byte, key *rsa.PublicKey) []byte {
z := new(big.Int).SetBytes(data)
e := big.NewInt(int64(key.E))
c := new(big.Int).Exp(z, e, key.N)
res := make([]byte, rsaLen)
c.FillBytes(res)
return res
}
func rsaDecrypt(data []byte, key *rsa.PrivateKey, to []byte) bool {
c := new(big.Int).SetBytes(data)
m := new(big.Int).Exp(c, key.D, key.N)
return FillBytes(m, to)
}