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 crypt As New Chilkat.Crypt2

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

Dim phcHash As String
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.
Dim json As New Chilkat.JsonObject
Dim success As Boolean
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.
Dim verifyResult As Int32
verifyResult = crypt.Argon2VerifyPassword(password,json.Emit(),phcHash)
If (verifyResult = 1) Then
    System.DebugLog("The password is verified.")
Else
    If (verifyResult = 0) Then
        System.DebugLog("The password does not match.")
    Else
        System.DebugLog("The verification could not be performed: " + crypt.LastErrorText)
    End If

End If