// key_to_struct
// Python version returns a string, but we use byte[] to get the same results
public static byte[] KeyToStruct(RsaParameters key)
{
byte[] modLength = { 0x00, 0x00, 0x00, 0x80 };
var mod = key.Modulus;
byte[] expLength = { 0x00, 0x00, 0x00, 0x03 };
var exponent = key.Exponent;
return(DataTypeUtils.CombineBytes(modLength, mod, expLength, exponent));
}
// key_from_b64
// BitConverter has different endianness, hence the Reverse()
public static RsaParameters KeyFromB64(string b64Key)
{
var decoded = Convert.FromBase64String(b64Key);
var modLength = BitConverter.ToInt32(decoded.Take(4).Reverse().ToArray(), 0);
var mod = decoded.Skip(4).Take(modLength).ToArray();
var expLength = BitConverter.ToInt32(decoded.Skip(modLength + 4).Take(4).Reverse().ToArray(), 0);
var exponent = decoded.Skip(modLength + 8).Take(expLength).ToArray();
var rsaKeyInfo = new RsaParameters
{
Modulus = mod,
Exponent = exponent
};
return(rsaKeyInfo);
}
// signature
public static string CreateSignature(string email, string password, RsaParameters key)
{
var rsa = AsymmetricKeyAlgorithmProvider.OpenAlgorithm(AsymmetricAlgorithmNames.RsaOaepSha1);
var keyBlob = CryptographicBuffer.DecodeFromBase64String(_b64KeyBlob);
var publicKey = rsa.ImportPublicKey(keyBlob, CryptographicPublicKeyBlobType.Capi1PublicKey);
byte[] prefix = { 0x00 };
var hashAlgorithm = HashAlgorithmProvider.OpenAlgorithm(HashAlgorithmNames.Sha1);
var hash = hashAlgorithm.HashData(KeyToStruct(key).AsBuffer()).ToArray().Take(4).ToArray();
var encrypted =
CryptographicEngine.Encrypt(publicKey, Encoding.UTF8.GetBytes(email + "\x00" + password).AsBuffer(),
null).ToArray();
return(DataTypeUtils.UrlSafeBase64(DataTypeUtils.CombineBytes(prefix, hash, encrypted)));
}