(PureBasic) Duplicate openssl dgst -sha256 -verify pubKey.pem -signature signature.sig in.dat

Demonstrates how to duplicate this OpenSSL command:

openssl dgst -sha256 -verify pubKey.pem -signature signature.sig in.dat

1. Creates a SHA256 digest of the contents of the input file.
2. Verifies the SHA256 digest using the public key.

Chilkat PureBasic Module Download Chilkat PureBasic Module

IncludeFile "CkBinData.pb"
IncludeFile "CkRsa.pb"
IncludeFile "CkPublicKey.pb"

Procedure ChilkatExample()

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

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

    ; Load the public key from an PEM file:
    success.i = CkPublicKey::ckLoadFromFile(pubKey,"pubKey.pem")
    If success <> 1
        Debug CkPublicKey::ckLastErrorText(pubKey)
        CkPublicKey::ckDispose(pubKey)
        ProcedureReturn
    EndIf

    ; Load the data of the original file that was signed.
    bdFileData.i = CkBinData::ckCreate()
    If bdFileData.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success = CkBinData::ckLoadFile(bdFileData,"in.dat")

    ; Load the signature.
    bdSig.i = CkBinData::ckCreate()
    If bdSig.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success = CkBinData::ckLoadFile(bdSig,"signature.sig")

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

    ; Import the public key into the RSA component:
    success = CkRsa::ckImportPublicKeyObj(rsa,pubKey)
    If success <> 1
        Debug CkRsa::ckLastErrorText(rsa)
        CkPublicKey::ckDispose(pubKey)
        CkBinData::ckDispose(bdFileData)
        CkBinData::ckDispose(bdSig)
        CkRsa::ckDispose(rsa)
        ProcedureReturn
    EndIf

    ; OpenSSL uses big-endian.
    CkRsa::setCkLittleEndian(rsa, 0)

    success = CkRsa::ckVerifyBd(rsa,bdFileData,"sha256",bdSig)
    If success <> 1
        Debug CkRsa::ckLastErrorText(rsa)
        Debug "The signature was invalid."
        CkPublicKey::ckDispose(pubKey)
        CkBinData::ckDispose(bdFileData)
        CkBinData::ckDispose(bdSig)
        CkRsa::ckDispose(rsa)
        ProcedureReturn
    EndIf

    Debug "The signature was verified."


    CkPublicKey::ckDispose(pubKey)
    CkBinData::ckDispose(bdFileData)
    CkBinData::ckDispose(bdSig)
    CkRsa::ckDispose(rsa)


    ProcedureReturn
EndProcedure