public bool Unpack(byte[] tag, byte[] plain)
{
byte[] internalBytes = NtagHelpers.GetInternalTag(tag);
// Generate keys
KeygenDerivedkeys dataKeys = GenerateKey(this.data, internalBytes);
KeygenDerivedkeys tagKeys = GenerateKey(this.tag, internalBytes);
// Decrypt
dataKeys.Cipher(internalBytes, plain, false);
// Init OpenSSL HMAC context
HMac hmacCtx = new HMac(new Sha256Digest());
// Regenerate tag HMAC. Note: order matters, data HMAC depends on tag HMAC!
hmacCtx.Init(new KeyParameter(tagKeys.hmacKey));
hmacCtx.BlockUpdate(plain, 0x1D4, 0x34);
hmacCtx.DoFinal(plain, HMAC_POS_TAG);
// Regenerate data HMAC
hmacCtx.Init(new KeyParameter(dataKeys.hmacKey));
hmacCtx.BlockUpdate(plain, 0x029, 0x1DF);
hmacCtx.DoFinal(plain, HMAC_POS_DATA);
Array.Copy(tag, 0x208, plain, 0x208, 0x014);
return
(NativeHelpers.MemCmp(plain, internalBytes, HMAC_POS_DATA, 32) &&
NativeHelpers.MemCmp(plain, internalBytes, HMAC_POS_TAG, 32));
}
protected bool Equals(KeygenDerivedkeys other)
{
return
(NativeHelpers.MemCmp(aesKey, other.aesKey, 0, aesKey.Length) &&
NativeHelpers.MemCmp(aesIV, other.aesIV, 0, aesIV.Length) &&
NativeHelpers.MemCmp(hmacKey, other.hmacKey, 0, hmacKey.Length));
}
