// Convert string to an RSA private key
func Base64ToPriv(s string) (*rsa.PrivateKey, os.Error) {
if len(s) == 0 {
return nil, nil
}
if !verifyCRC(s) {
return nil, nil
}
s = s[0 : len(s)-1]
enc := base64.StdEncoding
pk := rsa.PrivateKey{}
buf := make([]byte, 4096) // shoud be big enough
src := []byte(s)
k := -1
// N
if k = firstComma(src); k < 0 {
return nil, os.ErrorString("missing delimiter")
}
n, err := enc.Decode(buf, src[0:k])
if err != nil {
return nil, err
}
pk.N = &big.Int{}
pk.N.SetBytes(buf[0:n])
src = src[k+1:]
// E
if k = firstComma(src); k < 0 {
return nil, os.ErrorString("missing delimiter")
}
n, err = enc.Decode(buf, src[0:k])
if err != nil {
return nil, err
}
pke64, err := bytesToInt64(buf[0:n])
if err != nil {
return nil, err
}
pk.E = int(pke64)
src = src[k+1:]
// D
if k = firstComma(src); k < 0 {
return nil, os.ErrorString("missing delimiter")
}
n, err = enc.Decode(buf, src[0:k])
if err != nil {
return nil, err
}
pk.D = &big.Int{}
pk.D.SetBytes(buf[0:n])
src = src[k+1:]
// P
if k = firstComma(src); k < 0 {
return nil, os.ErrorString("missing delimiter")
}
n, err = enc.Decode(buf, src[0:k])
if err != nil {
return nil, err
}
pk.P = &big.Int{}
pk.P.SetBytes(buf[0:n])
src = src[k+1:]
// Q
n, err = enc.Decode(buf, src)
if err != nil {
return nil, err
}
pk.Q = &big.Int{}
pk.Q.SetBytes(buf[0:n])
return &pk, nil
}
func main() {
message := []byte("MODULUS")
message_p := []byte("PRIME Pea")
pb := make([]byte, 32)
pb[0] = 0x80
for i, c := range message {
pb[i] |= c >> 7
pb[i+1] |= c << 1
}
copy(pb[len(message)+2:], message_p)
p, err := PrimeWithPrefix(pb, 512)
if err != nil {
panic(err)
}
qb := make([]byte, 33)
message_q := []byte("PRIME Queue")
qb[0] = 0x80
copy(qb[len(message)+2:], message_q)
q, err := PrimeWithPrefix(qb, 512)
if err != nil {
panic(err)
}
n := big.NewInt(0)
n.Mul(p, q)
// To calculate the modulus from the desired private key, we need simply to
// invert it modulo (p-1)(q-1)
phi_p := big.NewInt(-1)
phi_p.Add(phi_p, p)
phi_q := big.NewInt(-1)
phi_q.Add(phi_q, q)
phi := big.NewInt(0)
phi.Mul(phi_p, phi_q)
d := big.NewInt(0x10001)
d.ModInverse(d, phi)
private := new(rsa.PrivateKey)
private.N = n
private.E = 0x10001
private.D = d
private.Primes = []*big.Int{p, q}
private.Precompute()
rfckey := rfc3441PrivateKey{Version: 0,
Modulus: n,
PublicExponent: 0x10001,
PrivateExponent: d,
Prime1: p, Prime2: q,
Exponent1: private.Precomputed.Dp,
Exponent2: private.Precomputed.Dq,
Coefficient: private.Precomputed.Qinv}
priv_enc, err := asn1.Marshal(rfckey)
if err != nil {
panic(err)
}
b := pem.Block{Type: "RSA PRIVATE KEY", Bytes: priv_enc}
pem.Encode(os.Stdout, &b)
}