C#

Verify an RSA Signature Against the Signed String

See more Apple Keychain Examples

Demonstrates how to validate an RSA Signature against the string that was signed. C#

bool success = false;

//  Create the same string we previously signed in this example: 
//  RSA Sign utf-8 Bytes of String to get Base64 RSA Signature

Chilkat.StringBuilder sb = new Chilkat.StringBuilder();
bool crlfLineEnding = true;
int i;
for (i = 0; i <= 10; i++) {
    sb.AppendLine("This is a test.",crlfLineEnding);
}

string base64_rsa_sig = "gWgpEXQqvXN6wh0MuFXPiw2xCb8cnmdizBT1TD1Tpm2GlJ8gnD59DGSj35GGXk1tM+mCOvMa2uW/9gmz8p6A90JLbn918i/2wKGvcde4wXnzPO7JADSNn2UwYzf3rp4/q/JrHv1GZETRJhABSFqTxOgdmdbEJQE/zijOSctCtQAM2CTb6t2BO8uHKSSUAwPH2cbeWxqsaVRLT4ruk5nZOxhoLgLMSjupiSzbE8zSTkkFOEHD+Mbb2xwg85AI0E4DsUnp+hLwwtS0blesgSyvtBY8oJODJeFcJsR7JDOTPdzHQHgJRl/2A4ij5xT91TpXy7ok43jhT6O9j7Q3qrafIQ==";

//  Get the public key to be used for signature verification.
Chilkat.PublicKey pubKey = new Chilkat.PublicKey();
success = pubKey.LoadFromFile("rsaKeys/chilkat-rsa-2048.pem");
if (success == false) {
    Debug.WriteLine(pubKey.LastErrorText);
    return;
}

Chilkat.Rsa rsa = new Chilkat.Rsa();
success = rsa.UsePublicKey(pubKey);
if (success == false) {
    Debug.WriteLine(rsa.LastErrorText);
    return;
}

//  Verify the string against the signature.
//  We signed the utf-8 byte representation of the string, so we must indicate
//  to also validate against the utf-8 byte representation.
rsa.Charset = "utf-8";
rsa.EncodingMode = "base64";
string signedString = sb.GetAsString();
success = rsa.VerifyStringENC(signedString,"sha256",base64_rsa_sig);

if (success == false) {
    Debug.WriteLine(rsa.LastErrorText);
    Debug.WriteLine("Signature invalid.");
}
else {
    Debug.WriteLine("Signature valid.");
}