(PureBasic) RSA Sign with PKCS8 Encrypted Key

Demonstrates how to load a private key from an encrypted PKCS8 file and create an RSA digital signature (and then verify it).

Note: This example requires Chilkat v11.0.0 or greater.

Chilkat PureBasic Module Download Chilkat PureBasic Module

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 PEM file:
    success = CkPrivateKey::ckLoadAnyFormatFile(privKey,"raul_privateKey.key","a0123456789")
    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

    ; This example will sign a string, and receive the signature
    ; in a hex-encoded string.  Therefore, set the encoding mode
    ; to "hex":
    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 sha1, sha384, sha512 and others.
    hexSig.s = CkRsa::ckSignStringENC(rsa,strData,"sha256")
    If CkRsa::ckLastMethodSuccess(rsa) = 0
        Debug CkRsa::ckLastErrorText(rsa)
        CkPrivateKey::ckDispose(privKey)
        CkRsa::ckDispose(rsa)
        ProcedureReturn
    EndIf

    Debug hexSig

    ; Now verify with the public key.
    ; This example shows how to use the public key from 
    ; a digital certificate (.cer file)
    cert.i = CkCert::ckCreate()
    If cert.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success = CkCert::ckLoadFromFile(cert,"raul_publicKey.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)

    rsa2.i = CkRsa::ckCreate()
    If rsa2.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    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

    ; Verify the signature against the original data:
    CkRsa::setCkEncodingMode(rsa2, "hex")
    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 "Signature verified!"

    ; Verify with incorrect data:
    success = CkRsa::ckVerifyStringENC(rsa2,"something else","sha256",hexSig)
    If success <> 1
        Debug "Signature not verified! (which was expected in this case)"
    Else
        Debug "Hmmm... that's not right..."
    EndIf



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


    ProcedureReturn
EndProcedure