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(DataFlex) Duplicate openssl rsautl -encrypt –in mytext.txt -out mytest.enc -inkey mycertificate.cer -certin –pkcs

Demonstrates how to duplicate this OpenSSL command:

openssl.exe  rsautl -encrypt –in mytext.txt -out mytest.enc -inkey mycertificate.cer -certin –pkcs

Important: The RSA encryption algorithm produces different results for each call, even when encrypting the same data with the same key. Decryption however, will produce the correct results. This example demonstrates.

The reason this occurs is that RSA encryption uses PKCS1 v1.5 padding, and this padding scheme uses random bytes. It is random bytes in the padding that causes the result to be different each time.

The mytext.txt file is a small file. (RSA can only be used to encrypt or sign small amounts of data.)

How much data can be encrypted with "openssl rsautl"? The maximum size (in bytes) is the key size minus the overhead for the padding. The overhead size depends on the padding. With OAEP padding, the overhead is 42 bytes. With the default PKCSv1.5 padding, the overhead is 11 bytes.

Given a 2048-bit RSA key (256 bytes) and using PKCSv1.5 padding, the max data size that can be signed is 256 - 11 = 245 bytes.

Chilkat ActiveX Downloads

ActiveX for 32-bit and 64-bit Windows

Use ChilkatAx-9.5.0-win32.pkg

Procedure Test
    Handle hoCert
    Boolean iSuccess
    Variant vBd
    Handle hoBd
    Handle hoRsa
    Variant vPubkey
    Handle hoPubkey
    Boolean iBUsePrivateKey
    String sTemp1

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

    Get Create (RefClass(cComChilkatCert)) To hoCert
    If (Not(IsComObjectCreated(hoCert))) Begin
        Send CreateComObject of hoCert
    End

    // Load the certificate from a file.
    Get ComLoadFromFile Of hoCert "mycertificate.cer" To iSuccess
    If (iSuccess <> True) Begin
        Get ComLastErrorText Of hoCert To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    // Load the file to be encrypted.
    Get Create (RefClass(cComChilkatBinData)) To hoBd
    If (Not(IsComObjectCreated(hoBd))) Begin
        Send CreateComObject of hoBd
    End
    Get ComLoadFile Of hoBd "mytext.txt" To iSuccess

    Get Create (RefClass(cComChilkatRsa)) To hoRsa
    If (Not(IsComObjectCreated(hoRsa))) Begin
        Send CreateComObject of hoRsa
    End

    // Get the cert's public key.
    Get ComExportPublicKey Of hoCert To vPubkey
    If (IsComObject(vPubkey)) Begin
        Get Create (RefClass(cComChilkatPublicKey)) To hoPubkey
        Set pvComObject Of hoPubkey To vPubkey
    End

    // Import the public key into the RSA component:
    Get ComImportPublicKeyObj Of hoRsa vPubkey To iSuccess
    If (iSuccess <> True) Begin
        Send Destroy of hoPubkey
        Get ComLastErrorText Of hoRsa To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    Send Destroy of hoPubkey

    // OpenSSL uses big-endian.
    Set ComLittleEndian Of hoRsa To False

    // Encrypt the contents of bd, replacing it with the encrypted data.
    Move False To iBUsePrivateKey
    Get pvComObject of hoBd to vBd
    Get ComEncryptBd Of hoRsa vBd iBUsePrivateKey To iSuccess
    If (iSuccess <> True) Begin
        Get ComLastErrorText Of hoRsa To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    // Save the RSA encrypted data to a file.
    Get ComWriteFile Of hoBd "mytest.enc" To iSuccess
    If (iSuccess <> True) Begin
        Showln "Failed to write RSA encrypted output file."
        Procedure_Return
    End

    Showln "Success."


End_Procedure

 

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