Verify an Argon2 Password with a Secret and Memory Guard

Demonstrates Crypt2.Argon2VerifyPassword when the hash was created with a secret (pepper) or ad, and the use of maxMemoryKb to guard against untrusted hash strings.

Dim fso, outFile
Set fso = CreateObject("Scripting.FileSystemObject")
'Create a Unicode (utf-16) output text file.
Set outFile = fso.CreateTextFile("output.txt", True, True)

set crypt = CreateObject("Chilkat.Crypt2")

'  The password should come from a secure source rather than being hard-coded.
password = "correct horse battery staple"

phcHash = "$argon2id$v=19$m=131072,t=4,p=2$c29tZXJhbmRvbXNhbHQ$3fJ7v1qKcVJ0lHqXjBQZ8mYm3sNTfSPRt0bqDl9kEyM"

'  When the hash was created with a secret (pepper) or ad, the same values must be supplied to verify.
'  Only the secret, ad, encoding, passwordCharset, and maxMemoryKb members of the options are used;
'  everything else is ignored.
set json = CreateObject("Chilkat.JsonObject")
success = json.UpdateString("secret","application-wide-pepper")
success = json.UpdateString("secretEncoding","utf-8")

'  maxMemoryKb guards against a hash from an untrusted source claiming an enormous memory cost.  The
'  memory cost is taken from the hash string, so this limit is checked before any memory is allocated.
'  It defaults to 2 GB.
success = json.UpdateInt("maxMemoryKb",262144)

'  Argon2VerifyPassword returns 1 if the password matched, 0 if it did not match, and -1 if the
'  verification could not be performed.  Always test for a match with == 1.
verifyResult = crypt.Argon2VerifyPassword(password,json.Emit(),phcHash)
If (verifyResult = 1) Then
    outFile.WriteLine("The password is verified.")
Else
    If (verifyResult = 0) Then
        outFile.WriteLine("The password does not match.")
    Else
        outFile.WriteLine("The verification could not be performed: " & crypt.LastErrorText)
    End If

End If


outFile.Close