(Excel) JWE using PBES2 Key Wrapping

Demonstrates how to create and decrypt a JWE that using PBES2 key wrapping.

This example demonstrates PBES2 with HMAC SHA-256 and A128KW wrapping. It is also possible to do the following by simply changing the "alg" parameter:

• PBES2 with HMAC SHA-384 and A192KW wrapping
• PBES2 with HMAC SHA-512 and A256KW wrapping

Note: This example requires Chilkat v9.5.0.66 or greater.

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

' Note: This example requires Chilkat v9.5.0.66 or greater.


plaintext = "Live long and prosper."

Dim jwe As Chilkat.Jwe
Set jwe = Chilkat.NewJwe

' First build the JWE Protected Header..
Dim jweProtHdr As Chilkat.JsonObject
Set jweProtHdr = Chilkat.NewJsonObject
Dim success As Boolean
success = jweProtHdr.AppendString("alg","PBES2-HS256+A128KW")
success = jweProtHdr.AppendString("enc","A128GCM")

' PBES2 requires two additional parameters:
' 1) A random salt parameter ("p2s") containing 8 or more bytes in base64url format.
' 2) An iteration count parameter ("p2c").  A minimum count of 1000 is recommended.
'    The iteration count is intended to make the PBES2 computation more expensive (time consuming)
'    to prevent brute-force attacks.
Dim prng As Chilkat.Prng
Set prng = Chilkat.NewPrng
success = jweProtHdr.AppendString("p2s",prng.GenRandom(16,"base64url"))
success = jweProtHdr.AppendString("p2c","1000")

Debug.Print "JWE Protected Header: "; jweProtHdr.Emit()
Debug.Print "--"

' Don't forget to actually provide the protected header to the JWE object:
success = jwe.SetProtectedHeader(jweProtHdr)

' Set the PBES2 password

recipientIndex = 0
success = jwe.SetPassword(recipientIndex,"top secret")

' Encrypt and return the JWE:

strJwe = jwe.Encrypt(plaintext,"utf-8")
If (jwe.LastMethodSuccess <> True) Then
    Debug.Print jwe.LastErrorText
    Exit Sub
End If

' Show the JWE we just created:
Debug.Print strJwe

' Decrypt the JWE.
Dim jwe2 As Chilkat.Jwe
Set jwe2 = Chilkat.NewJwe
success = jwe2.LoadJwe(strJwe)
If (success <> True) Then
    Debug.Print jwe2.LastErrorText
    Exit Sub
End If

' Set the PBES2 password
success = jwe2.SetPassword(recipientIndex,"top secret")

' Decrypt.

originalPlaintext = jwe2.Decrypt(0,"utf-8")
If (jwe2.LastMethodSuccess <> True) Then
    Debug.Print jwe2.LastErrorText
    Exit Sub
End If

Debug.Print "original text: "
Debug.Print originalPlaintext

' Sample output:

' JWE Protected Header: {"alg":"PBES2-HS256+A128KW","enc":"A128GCM","p2s":"z39rTEfRy1T1Yn_D1mZRlg","p2c":"1000"}
' --
' eyJhbGciOiJQQkVTMi1IUzI1NitBMTI4S1ciLCJlbmMiOiJBMTI4R0NNIiwicDJzIjoiejM5clRFZlJ5MVQxWW5fRDFtWlJsZyIsInAyYyI6IjEwMDAifQ.koYt6PrFmYwcwdcT7ZcvXHA1d-Xez5h4.luGlbvEnZp-7IsBOj42Yhw.YMTcfLf8Qe4zazozGV2OAu3cUdQ8Kg.rWub47ESWkc6IqZJTvSTmg
' original text: 
' Live long and prosper.