Visual FoxPro Requires Chilkat v11.6.0+

Argon2 Key Derivation with a Secret (Pepper), AD, and Encodings

Demonstrates the optional Argon2 options for Crypt2.Argon2DeriveKey: secret (a pepper), ad (associated data), the encoding member and its per-member overrides saltEncoding/secretEncoding/adEncoding, passwordCharset, and maxMemoryKb.

Background. A pepper is a secret value held by the application and not stored with the hash, so a stolen hash database cannot be attacked without it. The encoding members control how the salt, secret, and ad text are interpreted as bytes (base64 by default; utf-8 uses the characters themselves). maxMemoryKb is a guard against an unreasonable memory cost.

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LOCAL lnSuccess
LOCAL loCrypt
LOCAL lcPassword
LOCAL loJson
LOCAL loBdKey
LOCAL lcKeyHex

lnSuccess = 0

loCrypt = CreateObject('Chilkat.Crypt2')

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

*  Build the Argon2 options JSON, this time using the optional secret, ad, and encoding members.
*    secret         the RFC 9106 secret value K, often called a "pepper": a key held by the
*                   application and NOT stored with the hash, so a stolen hash database cannot be
*                   attacked without it.
*    ad             optional associated data X: additional non-secret data bound into the derivation.
*    encoding       how salt, secret, and ad are encoded (default base64).  Per-member overrides are
*                   saltEncoding, secretEncoding, and adEncoding.
*    passwordCharset  the charset the password is converted to before use (default utf-8).
*    maxMemoryKb    a guard (not an Argon2 parameter) refusing to allocate more than this many KB;
*                   default 2097152 (2 GB).
loJson = CreateObject('Chilkat.JsonObject')

*  The salt is provided here as hex, overriding the default base64 for just this member.
loJson.UpdateString("salt","0102030405060708090a0b0c0d0e0f10")
loJson.UpdateString("saltEncoding","hex")

*  The pepper is supplied as UTF-8 text (its own characters are the bytes).
loJson.UpdateString("secret","application-wide-pepper")
loJson.UpdateString("secretEncoding","utf-8")

*  Associated data, supplied as UTF-8 text.
loJson.UpdateString("ad","user-id-42")
loJson.UpdateString("adEncoding","utf-8")

loJson.UpdateString("passwordCharset","utf-8")
loJson.UpdateInt("maxMemoryKb",1048576)
loJson.UpdateInt("keyLen",32)

loBdKey = CreateObject('Chilkat.BinData')
lnSuccess = loCrypt.Argon2DeriveKey(lcPassword,loJson.Emit(),loBdKey)
IF (lnSuccess = 0) THEN
    ? loCrypt.LastErrorText
    RELEASE loCrypt
    RELEASE loJson
    RELEASE loBdKey
    CANCEL
ENDIF

lcKeyHex = loBdKey.GetEncoded("hex")
IF (loBdKey.LastMethodSuccess = 0) THEN
    ? loBdKey.LastErrorText
    RELEASE loCrypt
    RELEASE loJson
    RELEASE loBdKey
    CANCEL
ENDIF

? "Derived key: " + lcKeyHex

RELEASE loCrypt
RELEASE loJson
RELEASE loBdKey