PureBasic

Verify an RSA Signature Against the Signed Hash

See more Apple Keychain Examples

Demonstrates how to validate an RSA Signature against the hash that was signed. PureBasic

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

Procedure ChilkatExample()

    success.i = 0

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

    i.i
    For i = 0 To 100
        CkBinData::ckAppendEncoded(bd,"000102030405060708090A0B0C0D0E0F","hex")
    Next
    sha256_base64.s = CkBinData::ckGetHash(bd,"sha256","base64")
    Debug "sha256 hash in base64 format: " + sha256_base64

    base64_rsa_sig.s = "AwF2BbOvL6jA5DwmMAc9n6J2Cc8PI6Rj5W079+aKJcIEtPWRzHor0Bvc3aftGM3Jbgj6SXlIC3M3RYS7UZOnfiHKFNZgbxaNT5WwsWooK42ZkC8DBZl0p7OunBUKd5SciUo+TKilioeUkriN3L1Zl9hwi3HVDVqgVo3XXskwIftSqLSFlepTLTmOWj9Y93dp8J4D9RyLtNgFQBc0WB22tyJTsuY56mLcWe1AMF3LizB9OrbwjynF2u16xWlrJdugccz795fJBUV9aQSD+8S3KeqwQhoi8RK1uhD68aGCyaSpBq0NZ8COAkn7MXaF4POxrAAt8udfHM+PRfSOptcH/w=="

    ; 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)
        CkBinData::ckDispose(bd)
        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)
        CkBinData::ckDispose(bd)
        CkPublicKey::ckDispose(pubKey)
        CkRsa::ckDispose(rsa)
        ProcedureReturn
    EndIf

    ; Verify the hash against the signature.
    CkRsa::setCkEncodingMode(rsa, "base64")
    success = CkRsa::ckVerifyHashENC(rsa,sha256_base64,"sha256",base64_rsa_sig)

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



    CkBinData::ckDispose(bd)
    CkPublicKey::ckDispose(pubKey)
    CkRsa::ckDispose(rsa)


    ProcedureReturn
EndProcedure