method

scrypt

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What's this?

scrypt(p1, p2 = {}) public

Derives a key from pass using given parameters with the scrypt password-based key derivation function. The result can be used for password storage.

scrypt is designed to be memory-hard and more secure against brute-force attacks using custom hardwares than alternative KDFs such as PBKDF2 or bcrypt.

The keyword arguments N, r and p can be used to tune scrypt. RFC 7914 (published on 2016-08, tools.ietf.org/html/rfc7914#section-2) states that using values r=8 and p=1 appears to yield good results.

See RFC 7914 (tools.ietf.org/html/rfc7914) for more information.

Parameters

pass	Passphrase.
salt	Salt.
N	CPU/memory cost parameter. This must be a power of 2.
r	Block size parameter.
p	Parallelization parameter.
length	Length in octets of the derived key.

Example

pass = "password"
salt = SecureRandom.random_bytes(16)
dk = OpenSSL::KDF.scrypt(pass, salt: salt, N: 2**14, r: 8, p: 1, length: 32)
p dk #=> "\xDA\xE4\xE2...\x7F\xA1\x01T"

Show source

static VALUE
kdf_scrypt(int argc, VALUE *argv, VALUE self)
{
    VALUE pass, salt, opts, kwargs[5], str;
    static ID kwargs_ids[5];
    size_t len;
    uint64_t N, r, p, maxmem;

    if (!kwargs_ids[0]) {
        kwargs_ids[0] = rb_intern_const("salt");
        kwargs_ids[1] = rb_intern_const("N");
        kwargs_ids[2] = rb_intern_const("r");
        kwargs_ids[3] = rb_intern_const("p");
        kwargs_ids[4] = rb_intern_const("length");
    }
    rb_scan_args(argc, argv, "1:", &pass, &opts);
    rb_get_kwargs(opts, kwargs_ids, 5, 0, kwargs);

    StringValue(pass);
    salt = StringValue(kwargs[0]);
    N = NUM2UINT64T(kwargs[1]);
    r = NUM2UINT64T(kwargs[2]);
    p = NUM2UINT64T(kwargs[3]);
    len = NUM2LONG(kwargs[4]);
    /*
     * OpenSSL uses 32MB by default (if zero is specified), which is too small.
     * Let's not limit memory consumption but just let malloc() fail inside
     * OpenSSL. The amount is controllable by other parameters.
     */
    maxmem = SIZE_MAX;

    str = rb_str_new(0, len);
    if (!EVP_PBE_scrypt(RSTRING_PTR(pass), RSTRING_LEN(pass),
                        (unsigned char *)RSTRING_PTR(salt), RSTRING_LEN(salt),
                        N, r, p, maxmem, (unsigned char *)RSTRING_PTR(str), len))
        ossl_raise(eKDF, "EVP_PBE_scrypt");

    return str;
}

scrypt

Related methods

Parameters

Example