/// <summary>Opens a Box</summary>
/// <param name="cipherText"></param>
/// <param name="nonce">The 24 byte nonce.</param>
/// <param name="secretKey">The recipient's secret key.</param>
/// <param name="publicKey">The sender's public key.</param>
/// <returns>The decrypted message.</returns>
/// <exception cref="KeyOutOfRangeException"></exception>
/// <exception cref="NonceOutOfRangeException"></exception>
/// <exception cref="CryptographicException"></exception>
public static byte[] Open(byte[] cipherText, byte[] nonce, byte[] secretKey, byte[] publicKey)
{
//validate the length of the secret key
if (secretKey == null || secretKey.Length != SecretKeyBytes)
{
throw new KeyOutOfRangeException("secretKey", secretKey == null ? 0 : secretKey.Length,
string.Format("key must be {0} bytes in length.", SecretKeyBytes));
}
//validate the length of the public key
if (publicKey == null || publicKey.Length != PublicKeyBytes)
{
throw new KeyOutOfRangeException("publicKey", publicKey == null ? 0 : secretKey.Length,
string.Format("key must be {0} bytes in length.", PublicKeyBytes));
}
//validate the length of the nonce
if (nonce == null || nonce.Length != NONCE_BYTES)
{
throw new NonceOutOfRangeException("nonce", nonce == null ? 0 : nonce.Length,
string.Format("nonce must be {0} bytes in length.", NONCE_BYTES));
}
//check to see if there are MAC_BYTES of leading nulls, if so, trim.
//this is required due to an error in older versions.
if (cipherText[0] == 0)
{
//check to see if trim is needed
var trim = true;
for (var i = 0; i < MAC_BYTES - 1; i++)
{
if (cipherText[i] != 0)
{
trim = false;
break;
}
}
//if the leading MAC_BYTES are null, trim it off before going on.
if (trim)
{
var temp = new byte[cipherText.Length - MAC_BYTES];
Array.Copy(cipherText, MAC_BYTES, temp, 0, cipherText.Length - MAC_BYTES);
cipherText = temp;
}
}
var buffer = new byte[cipherText.Length - MAC_BYTES];
var ret = SodiumLibrary.crypto_box_open_easy(buffer, cipherText, cipherText.Length, nonce, publicKey,
secretKey);
if (ret != 0)
{
throw new CryptographicException("Failed to open PublicKeyBox");
}
return(buffer);
}