internal void EncryptAndSign(byte[] inputNullable, int id, EncryptedFieldIds fieldId, out byte[] encrypted, out byte[] hmac)
{
if (inputNullable == null)
{
encrypted = null;
hmac = null;
return;
}
if (inputNullable.Length > 65535)
{
throw new ArgumentException(nameof(inputNullable));
}
GetIVandKeys(id, fieldId, out var iv, out var aesKey, out var hmacKey);
// encode length of input and add padding, to make it good for AES
BinaryProcedures.CreateBinaryWriter(out var ms, out var w);
w.Write((ushort)inputNullable.Length);
w.Write(inputNullable);
var bytesInLastBlock = (int)ms.Position % CryptoLibraries.AesBlockSize;
if (bytesInLastBlock != 0)
{
var bytesRemainingTillFullAesBlock = CryptoLibraries.AesBlockSize - bytesInLastBlock;
w.Write(_cryptoLibrary.GetRandomBytes(bytesRemainingTillFullAesBlock));
}
var inputWithPadding = ms.ToArray();
encrypted = new byte[inputWithPadding.Length];
_cryptoLibrary.ProcessAesCbcBlocks(true, aesKey, iv, inputWithPadding, encrypted);
hmac = _cryptoLibrary.GetSha256HMAC(hmacKey, encrypted);
}
void GetIVandKeys(int id, EncryptedFieldIds fieldId, out byte[] iv, out byte[] aesKey, out byte[] hmacKey)
{
BinaryProcedures.CreateBinaryWriter(out var ms, out var w);
w.Write(id);
w.Write((byte)fieldId);
var sha256result = _cryptoLibrary.GetHashSHA256(ms.ToArray());
var preKey = _keyProvider.HsmOperation(sha256result);
_cryptoLibrary.DeriveKeysRFC5869_32bytes(preKey, sha256result, out aesKey, out hmacKey);
iv = sha256result.Take(16).ToArray();
}
internal byte[] DecryptAndVerify(byte[] encryptedNullable, byte[] hmacNullable, int id, EncryptedFieldIds fieldId)
{
if (encryptedNullable == null || hmacNullable == null)
{
return(null);
}
GetIVandKeys(id, fieldId, out var iv, out var aesKey, out var hmacKey);
var hmac = _cryptoLibrary.GetSha256HMAC(hmacKey, encryptedNullable);
if (!MiscProcedures.EqualByteArrays(hmacNullable, hmac))
{
throw new BadSignatureException();
}
var decrypted = new byte[encryptedNullable.Length];
_cryptoLibrary.ProcessAesCbcBlocks(false, aesKey, iv, encryptedNullable, decrypted);
using var reader = BinaryProcedures.CreateBinaryReader(decrypted, 0);
var dataLength = reader.ReadUInt16();
return(reader.ReadBytes(dataLength));
}
