C 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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#include <C_CkCrypt2.h>
#include <C_CkJsonObject.h>
#include <C_CkBinData.h>

void ChilkatSample(void)
    {
    BOOL success;
    HCkCrypt2 crypt;
    const char *password;
    HCkJsonObject json;
    HCkBinData bdKey;
    const char *keyHex;

    success = FALSE;

    crypt = CkCrypt2_Create();

    //  The password should come from a secure source rather than being hard-coded.
    password = "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).
    json = CkJsonObject_Create();

    //  The salt is provided here as hex, overriding the default base64 for just this member.
    CkJsonObject_UpdateString(json,"salt","0102030405060708090a0b0c0d0e0f10");
    CkJsonObject_UpdateString(json,"saltEncoding","hex");

    //  The pepper is supplied as UTF-8 text (its own characters are the bytes).
    CkJsonObject_UpdateString(json,"secret","application-wide-pepper");
    CkJsonObject_UpdateString(json,"secretEncoding","utf-8");

    //  Associated data, supplied as UTF-8 text.
    CkJsonObject_UpdateString(json,"ad","user-id-42");
    CkJsonObject_UpdateString(json,"adEncoding","utf-8");

    CkJsonObject_UpdateString(json,"passwordCharset","utf-8");
    CkJsonObject_UpdateInt(json,"maxMemoryKb",1048576);
    CkJsonObject_UpdateInt(json,"keyLen",32);

    bdKey = CkBinData_Create();
    success = CkCrypt2_Argon2DeriveKey(crypt,password,CkJsonObject_emit(json),bdKey);
    if (success == FALSE) {
        printf("%s\n",CkCrypt2_lastErrorText(crypt));
        CkCrypt2_Dispose(crypt);
        CkJsonObject_Dispose(json);
        CkBinData_Dispose(bdKey);
        return;
    }

    keyHex = CkBinData_getEncoded(bdKey,"hex");
    if (CkBinData_getLastMethodSuccess(bdKey) == FALSE) {
        printf("%s\n",CkBinData_lastErrorText(bdKey));
        CkCrypt2_Dispose(crypt);
        CkJsonObject_Dispose(json);
        CkBinData_Dispose(bdKey);
        return;
    }

    printf("Derived key: %s\n",keyHex);


    CkCrypt2_Dispose(crypt);
    CkJsonObject_Dispose(json);
    CkBinData_Dispose(bdKey);

    }