(Lianja) Encrypt a file to a PKCS7 encrypted message using multiple certificates from different users

Demonstrates how to encrypt a file to a PKCS7 encrypted message using multiple certificates from different users. Any one of the users can decrypt using his/her own certificate + private key.

Note: When doing public key encryption, it is the public key that is used to encrypt. The private key is required for decryption.

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

loCrypt = createobject("CkCrypt2")

//  Tell the crypt object to use 3 certificates.
//  Do this by calling AddEncryptCert for each certificate.

//  Load a digital certificate.
//  We don't need the private key for encryption.
//  Only the public key is needed (which is included in a certificate).
loCert1 = createobject("CkCert")
llSuccess = loCert1.LoadFromFile("qa_data/user1/cert_user1.pem")
//  Assume success for the example, but make sure your application checks for success/failure...
loCrypt.AddEncryptCert(loCert1)

loCert2 = createobject("CkCert")
llSuccess = loCert2.LoadFromFile("qa_data/user2/cert_user2.pem")
loCrypt.AddEncryptCert(loCert2)

loCert3 = createobject("CkCert")
llSuccess = loCert3.LoadFromFile("qa_data/user3/cert_user3.pem")
loCrypt.AddEncryptCert(loCert3)

//  Indicate that we want PKI encryption (i.e. public-key infrastructure)
//  to produce a CMS message (Cryptographic Message Syntax/PKCS7),
//  that is be created with RSAES-OAEP padding, SHA256, and AES-128 for the
//  bulk encryption.
loCrypt.CryptAlgorithm = "pki"
loCrypt.Pkcs7CryptAlg = "aes"
loCrypt.KeyLength = 128
loCrypt.OaepHash = "sha256"
loCrypt.OaepPadding = .T.

//  Load the file to be encrypted...
loFileData = createobject("CkBinData")
llSuccess = loFileData.LoadFile("qa_data/jpg/penguins.jpg")
//  Your app should check for success/failure..

//  Encrypt the data.  The contents of the fileData object are replaced with the PKCS7 encrypted message.
llSuccess = loCrypt.EncryptBd(loFileData)
if (llSuccess <> .T.) then
    ? loCrypt.LastErrorText
    release loCrypt
    release loCert1
    release loCert2
    release loCert3
    release loFileData
    return
endif

//  Save the PKCS7 encrypted message to a file..
llSuccess = loFileData.WriteFile("qa_output/pkcs7_encrypted.p7")

//  Now indicate that the PKCS7 output is to be returned in the base64 encoding.
loCrypt.EncodingMode = "base64"

? "OK."


release loCrypt
release loCert1
release loCert2
release loCert3
release loFileData