Key derivation. More...

#include <gcrypt.h>
#include "platform.h"
#include "gnunet_crypto_lib.h"

Include dependency graph for crypto_kdf.c:

Macros
#define	LOG(kind, ...) GNUNET_log_from (kind, "util-crypto-kdf", __VA_ARGS__)

Functions
int	GNUNET_CRYPTO_kdf_v (void result, size_t out_len, const void xts, size_t xts_len, const void *skm, size_t skm_len, va_list argp)
	Derive key. More...

int	GNUNET_CRYPTO_kdf (void result, size_t out_len, const void xts, size_t xts_len, const void *skm, size_t skm_len,...)
	Derive key. More...

void	GNUNET_CRYPTO_kdf_mod_mpi (gcry_mpi_t r, gcry_mpi_t n, const void xts, size_t xts_len, const void skm, size_t skm_len, const char ctx)
	Deterministically generate a pseudo-random number uniformly from the integers modulo a libgcrypt mpi. More...

Detailed Description

Key derivation.

Author: Nils Durner; Jeffrey Burdges burdg.nosp@m.es@g.nosp@m.nunet.nosp@m..org

Definition in file crypto_kdf.c.

Macro Definition Documentation

◆ LOG

#define LOG	(	kind,
		...
	)	GNUNET_log_from (kind, "util-crypto-kdf", __VA_ARGS__)

Definition at line 33 of file crypto_kdf.c.

Function Documentation

◆ GNUNET_CRYPTO_kdf_v()

int GNUNET_CRYPTO_kdf_v	(	void *	result,
		size_t	out_len,
		const void *	xts,
		size_t	xts_len,
		const void *	skm,
		size_t	skm_len,
		va_list	argp
	)

Derive key.

Parameters

result	buffer for the derived key, allocated by caller
out_len	desired length of the derived key
xts	salt
xts_len	length of xts
skm	source key material
skm_len	length of skm
argp	va_list of void * & size_t pairs for context chunks

Returns: GNUNET_YES on success

Definition at line 47 of file crypto_kdf.c.

References GNUNET_CRYPTO_hkdf_v().

Referenced by GNUNET_CRYPTO_hmac_derive_key_v(), GNUNET_CRYPTO_kdf(), and GNUNET_CRYPTO_symmetric_derive_iv_v().

 {
   /*
    * "Finally, we point out to a particularly advantageous instantiation using
    * HMAC-SHA512 as XTR and HMAC-SHA256 in PRF* (in which case the output from SHA-512 is
    * truncated to 256 bits). This makes sense in two ways: First, the extraction part is where we need a
    * stronger hash function due to the unconventional demand from the hash function in the extraction
    * setting. Second, as shown in Section 6, using HMAC with a truncated output as an extractor
    * allows to prove the security of HKDF under considerably weaker assumptions on the underlying
    * hash function."
    *
    * http://eprint.iacr.org/2010/264
    *///
   return GNUNET_CRYPTO_hkdf_v (result,
                                out_len,
                                GCRY_MD_SHA512,
                                GCRY_MD_SHA256,
                                xts,
                                xts_len,
                                skm,
                                skm_len,
                                argp);
 }

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◆ GNUNET_CRYPTO_kdf_mod_mpi()

void GNUNET_CRYPTO_kdf_mod_mpi	(	gcry_mpi_t *	r,
		gcry_mpi_t	n,
		const void *	xts,
		size_t	xts_len,
		const void *	skm,
		size_t	skm_len,
		const char *	ctx
	)

Deterministically generate a pseudo-random number uniformly from the integers modulo a libgcrypt mpi.

Parameters

[out]	r	MPI value set to the FDH
	n	MPI to work modulo
	xts	salt
	xts_len	length of xts
	skm	source key material
	skm_len	length of skm
	ctx	context string

Definition at line 127 of file crypto_kdf.c.

References buf, GNUNET_assert, GNUNET_CRYPTO_kdf(), and GNUNET_YES.

Referenced by rsa_blinding_key_derive(), and rsa_full_domain_hash().

 {
   gcry_error_t rc;
   unsigned int nbits;
   size_t rsize;
   uint16_t ctr;
 
   nbits = gcry_mpi_get_nbits (n);
   /* GNUNET_assert (nbits > 512); */
 
   ctr = 0;
   while (1)
   {
     /* Ain't clear if n is always divisible by 8 */
     uint8_t buf[ (nbits - 1) / 8 + 1 ];
     uint16_t ctr_nbo = htons (ctr);
 
     rc = GNUNET_CRYPTO_kdf (buf,
                             sizeof(buf),
                             xts, xts_len,
                             skm, skm_len,
                             ctx, strlen (ctx),
                             &ctr_nbo, sizeof(ctr_nbo),
                             NULL, 0);
     GNUNET_assert (GNUNET_YES == rc);
 
     rc = gcry_mpi_scan (r,
                         GCRYMPI_FMT_USG,
                         (const unsigned char *) buf,
                         sizeof(buf),
                         &rsize);
     GNUNET_assert (0 == rc);  /* Allocation error? */
 
     gcry_mpi_clear_highbit (*r, nbits);
     GNUNET_assert (0 == gcry_mpi_test_bit (*r, nbits));
     ++ctr;
     /* We reject this FDH if either *r > n and retry with another ctr */
     if (0 > gcry_mpi_cmp (*r, n))
       break;
     gcry_mpi_release (*r);
   }
 }