(Excel) 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.

Download Excel Class Modules Chilkat Excel Class Modules

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

Dim crypt As Chilkat.Crypt2
Set crypt = Chilkat.NewCrypt2

'  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).
Dim cert1 As Chilkat.Cert
Set cert1 = Chilkat.NewCert

success = cert1.LoadFromFile("qa_data/user1/cert_user1.pem")
'  Assume success for the example, but make sure your application checks for success/failure...
crypt.AddEncryptCert cert1

Dim cert2 As Chilkat.Cert
Set cert2 = Chilkat.NewCert
success = cert2.LoadFromFile("qa_data/user2/cert_user2.pem")
crypt.AddEncryptCert cert2

Dim cert3 As Chilkat.Cert
Set cert3 = Chilkat.NewCert
success = cert3.LoadFromFile("qa_data/user3/cert_user3.pem")
crypt.AddEncryptCert cert3

'  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.
crypt.CryptAlgorithm = "pki"
crypt.Pkcs7CryptAlg = "aes"
crypt.KeyLength = 128
crypt.OaepHash = "sha256"
crypt.OaepPadding = True

'  Load the file to be encrypted...
Dim fileData As Chilkat.BinData
Set fileData = Chilkat.NewBinData
success = fileData.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.
success = crypt.EncryptBd(fileData)
If (success <> True) Then
    Debug.Print crypt.LastErrorText
    Exit Sub
End If

'  Save the PKCS7 encrypted message to a file..
success = fileData.WriteFile("qa_output/pkcs7_encrypted.p7")

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

Debug.Print "OK."