PureBasic

RSA Signature/Verify with .key and .cer

See more RSA Examples

Demonstrates how to use a .key file (private key) and digital certificate (.cer, public key) to create and verify an RSA signature. PureBasic

IncludeFile "CkCert.pb"
IncludeFile "CkPublicKey.pb"
IncludeFile "CkPrivateKey.pb"
IncludeFile "CkRsa.pb"

Procedure ChilkatExample()

    success.i = 0

    ; This example assumes the Chilkat API to have been previously unlocked.
    ; See Global Unlock Sample for sample code.

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

    ; Load the private key from an RSA .key file:
    success = CkPrivateKey::ckLoadPemFile(privKey,"privateKey.key")
    If success = 0
        Debug CkPrivateKey::ckLastErrorText(privKey)
        CkPrivateKey::ckDispose(privKey)
        ProcedureReturn
    EndIf

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

    ; Import the private key into the RSA component:
    success = CkRsa::ckUsePrivateKey(rsa,privKey)
    If success = 0
        Debug CkRsa::ckLastErrorText(rsa)
        CkPrivateKey::ckDispose(privKey)
        CkRsa::ckDispose(rsa)
        ProcedureReturn
    EndIf

    ; Create the signature as a hex string:
    CkRsa::setCkEncodingMode(rsa, "hex")

    strData.s = "This is the string to be signed."

    ; Sign the string using the sha256 hash algorithm.
    ; Other valid choices are "md2", "sha1", "sha384",
    ; "sha512", and "md5".
    hexSig.s = CkRsa::ckSignStringENC(rsa,strData,"sha256")

    Debug hexSig

    ; Load a digital certificate from a .cer file:
    cert.i = CkCert::ckCreate()
    If cert.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success = CkCert::ckLoadFromFile(cert,"myCert.cer")
    If success = 0
        Debug CkCert::ckLastErrorText(cert)
        CkPrivateKey::ckDispose(privKey)
        CkRsa::ckDispose(rsa)
        CkCert::ckDispose(cert)
        ProcedureReturn
    EndIf

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

    CkCert::ckGetPublicKey(cert,pubKey)

    ; Now verify using a new instance of the RSA object:
    rsa2.i = CkRsa::ckCreate()
    If rsa2.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    ; Import the public key into the RSA object:
    success = CkRsa::ckUsePublicKey(rsa2,pubKey)
    If success = 0
        Debug CkRsa::ckLastErrorText(rsa2)
        CkPrivateKey::ckDispose(privKey)
        CkRsa::ckDispose(rsa)
        CkCert::ckDispose(cert)
        CkPublicKey::ckDispose(pubKey)
        CkRsa::ckDispose(rsa2)
        ProcedureReturn
    EndIf

    ; The signature is a hex string, so make sure the EncodingMode is correct:
    CkRsa::setCkEncodingMode(rsa2, "hex")

    ; Verify the signature:
    success = CkRsa::ckVerifyStringENC(rsa2,strData,"sha256",hexSig)
    If success = 0
        Debug CkRsa::ckLastErrorText(rsa2)
        CkPrivateKey::ckDispose(privKey)
        CkRsa::ckDispose(rsa)
        CkCert::ckDispose(cert)
        CkPublicKey::ckDispose(pubKey)
        CkRsa::ckDispose(rsa2)
        ProcedureReturn
    EndIf

    Debug "Success."


    CkPrivateKey::ckDispose(privKey)
    CkRsa::ckDispose(rsa)
    CkCert::ckDispose(cert)
    CkPublicKey::ckDispose(pubKey)
    CkRsa::ckDispose(rsa2)


    ProcedureReturn
EndProcedure