(Visual FoxPro) 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.

Chilkat ActiveX Downloads ActiveX for 32-bit and 64-bit Windows

LOCAL loSb
LOCAL lnCrlfLineEnding
LOCAL i
LOCAL lcBase64_rsa_sig
LOCAL loPubKey
LOCAL lnSuccess
LOCAL loRsa
LOCAL lcSignedString

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

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.StringBuilder')
loSb = CreateObject('Chilkat.StringBuilder')
lnCrlfLineEnding = 1

FOR i = 0 TO 10
    loSb.AppendLine("This is a test.",lnCrlfLineEnding)
NEXT

lcBase64_rsa_sig = "gWgpEXQqvXN6wh0MuFXPiw2xCb8cnmdizBT1TD1Tpm2GlJ8gnD59DGSj35GGXk1tM+mCOvMa2uW/9gmz8p6A90JLbn918i/2wKGvcde4wXnzPO7JADSNn2UwYzf3rp4/q/JrHv1GZETRJhABSFqTxOgdmdbEJQE/zijOSctCtQAM2CTb6t2BO8uHKSSUAwPH2cbeWxqsaVRLT4ruk5nZOxhoLgLMSjupiSzbE8zSTkkFOEHD+Mbb2xwg85AI0E4DsUnp+hLwwtS0blesgSyvtBY8oJODJeFcJsR7JDOTPdzHQHgJRl/2A4ij5xT91TpXy7ok43jhT6O9j7Q3qrafIQ=="

* Get the public key to be used for signature verification.
* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.PublicKey')
loPubKey = CreateObject('Chilkat.PublicKey')
lnSuccess = loPubKey.LoadFromFile("rsaKeys/chilkat-rsa-2048.pem")
IF (lnSuccess = 0) THEN
    ? loPubKey.LastErrorText
    RELEASE loSb
    RELEASE loPubKey
    CANCEL
ENDIF

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.Rsa')
loRsa = CreateObject('Chilkat.Rsa')
loRsa.ImportPublicKeyObj(loPubKey)

* 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.
loRsa.Charset = "utf-8"
loRsa.EncodingMode = "base64"
lcSignedString = loSb.GetAsString()
lnSuccess = loRsa.VerifyStringENC(lcSignedString,"sha256",lcBase64_rsa_sig)

IF (lnSuccess = 0) THEN
    ? loRsa.LastErrorText
    ? "Signature invalid."
ELSE
    ? "Signature valid."
ENDIF

RELEASE loSb
RELEASE loPubKey
RELEASE loRsa