public static byte[] _CustomEncryptCbcPkcs7(ReadOnlySpan <byte> data, ReadOnlySpan <byte> iv, byte[] key)
{
var len = data.Length / 16 + 1;
var output = new byte[len * 16];
var prevBlock = iv;
int i = 0;
for (; i < len - 1; i++)
{
var xored = Xor.ApplyFixed(prevBlock, data.Slice(i * 16, 16));
var encrypted = EncryptEcb(xored, key, PaddingMode.None);
Array.Copy(encrypted, 0, output, i * 16, 16);
prevBlock = encrypted;
}
var padded = PKCS7.Pad(data.Slice(i * 16, data.Length % 16), 16);
Array.Copy(EncryptEcb(Xor.ApplyFixed(prevBlock, padded), key), 0, output, i * 16, 16);
return(output);
}
public static ReadOnlySpan <byte> _CustomDecryptCbcPkcs7(ReadOnlySpan <byte> cipher, ReadOnlySpan <byte> iv, byte[] key)
{
var blocks = cipher.Length / 16;
var output = new byte[cipher.Length];
for (int i = blocks - 1; i >= 0; --i)
{
ReadOnlySpan <byte> prevBlock;
if (i == 0)
{
prevBlock = iv;
}
else
{
prevBlock = cipher.Slice((i - 1) * 16, 16);
}
var decryptedBlock = DecryptEcb(cipher.Slice(i * 16, 16), key, PaddingMode.None);
var xored = Xor.ApplyFixed(prevBlock, decryptedBlock);
Array.Copy(xored, 0, output, i * 16, 16);
}
return(PKCS7.StripPad(output));
}