JavaScript

Verify an RSA Signature Against the Signed String

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

var success = false;

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

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

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

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

var rsa = new CkRsa();
success = rsa.UsePublicKey(pubKey);
if (success == false) {
    console.log(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";
var signedString = sb.GetAsString();
success = rsa.VerifyStringENC(signedString,"sha256",base64_rsa_sig);

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