(Visual FoxPro) Duplicate openssl rsautl -sign -in small.dat -inkey private.pem -out rsautl.sig

Demonstrates how to duplicate this OpenSSL command:

openssl rsautl -sign -in small.dat -inkey private.pem -out rsautl.sig

The small.dat file is a small file that can contain text or binary data of any type. The "openssl rsautl" command is different than "openssl dgst -sign" because it signs the input data directly with the RSA algorithm. The "openssl dgst -sign" command first digests the input data and then signs the digest.

How much data can be signed 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

LOCAL loPkey
LOCAL lnSuccess
LOCAL loBd
LOCAL loRsa

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

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.PrivateKey')
loPkey = CreateObject('Chilkat.PrivateKey')

* Load the private key from an PEM file:
lnSuccess = loPkey.LoadPemFile("private.pem")
IF (lnSuccess <> 1) THEN
    ? loPkey.LastErrorText
    RELEASE loPkey
    CANCEL
ENDIF

* Load the file to be signed.
* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.BinData')
loBd = CreateObject('Chilkat.BinData')
lnSuccess = loBd.LoadFile("small.dat")

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.Rsa')
loRsa = CreateObject('Chilkat.Rsa')

* Import the private key into the RSA component:
lnSuccess = loRsa.ImportPrivateKeyObj(loPkey)
IF (lnSuccess <> 1) THEN
    ? loRsa.LastErrorText
    RELEASE loPkey
    RELEASE loBd
    RELEASE loRsa
    CANCEL
ENDIF

* OpenSSL uses big-endian.
loRsa.LittleEndian = 0

* Sign bd.  If successful, bd will contain the RSA signature that contains the original data.
lnSuccess = loRsa.OpenSslSignBd(loBd)
IF (lnSuccess <> 1) THEN
    ? loRsa.LastErrorText
    RELEASE loPkey
    RELEASE loBd
    RELEASE loRsa
    CANCEL
ENDIF

* Save the binary signature to a file.
lnSuccess = loBd.WriteFile("rsautl.sig")
IF (lnSuccess <> 1) THEN
    ? "Failed to save output signature file."
    RELEASE loPkey
    RELEASE loBd
    RELEASE loRsa
    CANCEL
ENDIF

? "Success."

RELEASE loPkey
RELEASE loBd
RELEASE loRsa