PureBasic

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. PureBasic

IncludeFile "CkStringBuilder.pb"
IncludeFile "CkRsa.pb"
IncludeFile "CkPublicKey.pb"

Procedure ChilkatExample()

    success.i = 0

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

    sb.i = CkStringBuilder::ckCreate()
    If sb.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    crlfLineEnding.i = 1
    i.i
    For i = 0 To 10
        CkStringBuilder::ckAppendLine(sb,"This is a test.",crlfLineEnding)
    Next

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

    ; Get the public key to be used for signature verification.
    pubKey.i = CkPublicKey::ckCreate()
    If pubKey.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success = CkPublicKey::ckLoadFromFile(pubKey,"rsaKeys/chilkat-rsa-2048.pem")
    If success = 0
        Debug CkPublicKey::ckLastErrorText(pubKey)
        CkStringBuilder::ckDispose(sb)
        CkPublicKey::ckDispose(pubKey)
        ProcedureReturn
    EndIf

    rsa.i = CkRsa::ckCreate()
    If rsa.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success = CkRsa::ckUsePublicKey(rsa,pubKey)
    If success = 0
        Debug CkRsa::ckLastErrorText(rsa)
        CkStringBuilder::ckDispose(sb)
        CkPublicKey::ckDispose(pubKey)
        CkRsa::ckDispose(rsa)
        ProcedureReturn
    EndIf

    ; 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.
    CkRsa::setCkCharset(rsa, "utf-8")
    CkRsa::setCkEncodingMode(rsa, "base64")
    signedString.s = CkStringBuilder::ckGetAsString(sb)
    success = CkRsa::ckVerifyStringENC(rsa,signedString,"sha256",base64_rsa_sig)

    If success = 0
        Debug CkRsa::ckLastErrorText(rsa)
        Debug "Signature invalid."
    Else
        Debug "Signature valid."
    EndIf



    CkStringBuilder::ckDispose(sb)
    CkPublicKey::ckDispose(pubKey)
    CkRsa::ckDispose(rsa)


    ProcedureReturn
EndProcedure