/// <summary>
/// Compare two IDEscrowPrivateKey objects.
/// </summary>
/// <param name="sk2">The object to compare against.</param>
/// <returns>True if equal, false otherwise.</returns>
public bool Equals(IDEscrowPrivateKey sk2)
{
if (sk2 == null)
{
return(false);
}
if (!sk2.X.Equals(this.x))
{
return(false);
}
return(true);
}
/// <summary>
/// Checks that <c>sk</c> is consistent with this public key and <c>param</c>.
/// </summary>
/// <returns><c>true</c> if valid, <c>false</c> otherwise.</returns>
public bool Verify(IDEscrowParams param, IDEscrowPrivateKey sk)
{
if (!param.ip.Zq.IsElement(sk.X)) // is x in the right field?
{
return(false);
}
GroupElement hPrime = param.Ge.Exponentiate(sk.X);
if (!hPrime.Equals(h)) // is h = ge^x ?
{
return(false);
}
return(true);
}
/// <summary>
/// Decrypts an ID escrow ciphertext without verifying the proof.
/// The proof must be verified by <c>IEFunctions.Verify</c> before decryption.
/// The IEVerifier verification step also checks the validity of
/// the ciphertext.
/// </summary>
/// <param name="ctext">Ciphertext to be decrypted</param>
/// <param name="sk"> Decryption key.</param>
/// <param name="ip"> Issuer paramters associated with the ID escrow scheme.</param>
/// <returns></returns>
/// <remarks>
/// Semantic verification of the label (the <c>additionalInfo</c> field of <c>ctext</c>),
/// i.e., whether it makes sense for the application is assumed to be done out-of-band.
/// For example, the application may check that the label includes a timestamp, and that
/// this timestamp falls within a given interval.
///
/// The IssuerParameters for decryption should match the issuer paramters used to create
/// the IEParam object used for decryption (i.e., IEParam.ip).
/// </remarks>
public static GroupElement Decrypt(IDEscrowParams param, IDEscrowCiphertext ctext, IDEscrowPrivateKey sk)
{
if (ctext == null || sk == null || param == null)
{
throw new ArgumentNullException("null input to Decrypt");
}
Group G = param.ip.Gq;
if (!IsGroupElement(G, ctext.E1) || !IsGroupElement(G, ctext.E2)) // this should never fail if Verify is called first, but we check again anyway.
{
throw new ArgumentException("E1 or E2 is not a valid group element in Decrypt");
}
GroupElement PE = ctext.E1.Exponentiate(sk.X.Negate()); // PE = E1^(-x) = H^(-r)
PE = PE.Multiply(ctext.E2); // PE = E2/E1^(x)
return(PE);
}
/// <summary>
/// Constructs a public key from the private key.
/// </summary>
public IDEscrowPublicKey(IDEscrowParams param, IDEscrowPrivateKey priv)
{
h = param.Ge.Exponentiate(priv.X); // H = (g_e)^x
}
