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srp.h
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srp.h
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/*
* Secure Remote Password 6a implementation
* https://github.com/est31/csrp-gmp
*
* The MIT License (MIT)
*
* Copyright (c) 2010, 2013 Tom Cocagne, 2015 est31 <MTest31@outlook.com>
*
* Permission is hereby granted, free of charge, to any person obtaining a copy of
* this software and associated documentation files (the "Software"), to deal in
* the Software without restriction, including without limitation the rights to
* use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
* of the Software, and to permit persons to whom the Software is furnished to do
* so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in all
* copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*
*/
/*
*
* Purpose: This is a direct implementation of the Secure Remote Password
* Protocol version 6a as described by
* http://srp.stanford.edu/design.html
*
* Author: tom.cocagne@gmail.com (Tom Cocagne)
*
* Dependencies: LibGMP
*
* Usage: Refer to test_srp.c for a demonstration
*
* Notes:
* This library allows multiple combinations of hashing algorithms and
* prime number constants. For authentication to succeed, the hash and
* prime number constants must match between
* srp_create_salted_verification_key(), srp_user_new(),
* and srp_verifier_new(). A recommended approach is to determine the
* desired level of security for an application and globally define the
* hash and prime number constants to the predetermined values.
*
* As one might suspect, more bits means more security. As one might also
* suspect, more bits also means more processing time. The test_srp.c
* program can be easily modified to profile various combinations of
* hash & prime number pairings.
*/
#ifndef SRP_H
#define SRP_H
struct SRPVerifier;
struct SRPUser;
typedef enum {
SRP_NG_1024,
SRP_NG_2048,
SRP_NG_4096,
SRP_NG_8192,
SRP_NG_CUSTOM
} SRP_NGType;
typedef enum {
SRP_SHA1,
/*SRP_SHA224,*/
SRP_SHA256,
/*SRP_SHA384,
SRP_SHA512*/
} SRP_HashAlgorithm;
typedef enum {
SRP_ERR,
SRP_OK,
} SRP_Result;
// clang-format off
/* Sets the memory functions used by srp.
* Note: this doesn't set the memory functions used by gmp,
* but it is supported to have different functions for srp and gmp.
* Don't call this after you have already allocated srp structures.
*/
void srp_set_memory_functions(
void *(*new_srp_alloc) (size_t),
void *(*new_srp_realloc) (void *, size_t),
void (*new_srp_free) (void *));
/* Out: bytes_v, len_v
*
* The caller is responsible for freeing the memory allocated for bytes_v
*
* The n_hex and g_hex parameters should be 0 unless SRP_NG_CUSTOM is used for ng_type.
* If provided, they must contain ASCII text of the hexidecimal notation.
*
* If bytes_s == NULL, it is filled with random data.
* The caller is responsible for freeing.
*
* Returns SRP_OK on success, and SRP_ERR on error.
* bytes_s might be in this case invalid, don't free it.
*/
SRP_Result srp_create_salted_verification_key(SRP_HashAlgorithm alg,
SRP_NGType ng_type, const char *username_for_verifier,
const unsigned char *password, size_t len_password,
unsigned char **bytes_s, size_t *len_s,
unsigned char **bytes_v, size_t *len_v,
const char *n_hex, const char *g_hex);
/* Out: bytes_B, len_B.
*
* On failure, bytes_B will be set to NULL and len_B will be set to 0
*
* The n_hex and g_hex parameters should be 0 unless SRP_NG_CUSTOM is used for ng_type
*
* If bytes_b == NULL, random data is used for b.
*
* Returns pointer to SRPVerifier on success, and NULL on error.
*/
struct SRPVerifier* srp_verifier_new(SRP_HashAlgorithm alg, SRP_NGType ng_type,
const char *username,
const unsigned char *bytes_s, size_t len_s,
const unsigned char *bytes_v, size_t len_v,
const unsigned char *bytes_A, size_t len_A,
const unsigned char *bytes_b, size_t len_b,
unsigned char** bytes_B, size_t *len_B,
const char* n_hex, const char* g_hex);
// clang-format on
void srp_verifier_delete(struct SRPVerifier *ver);
// srp_verifier_verify_session must have been called before
int srp_verifier_is_authenticated(struct SRPVerifier *ver);
const char *srp_verifier_get_username(struct SRPVerifier *ver);
/* key_length may be null */
const unsigned char *srp_verifier_get_session_key(
struct SRPVerifier *ver, size_t *key_length);
size_t srp_verifier_get_session_key_length(struct SRPVerifier *ver);
/* Verifies session, on success, it writes bytes_HAMK.
* user_M must be exactly srp_verifier_get_session_key_length() bytes in size
*/
void srp_verifier_verify_session(
struct SRPVerifier *ver, const unsigned char *user_M, unsigned char **bytes_HAMK);
/*******************************************************************************/
/* The n_hex and g_hex parameters should be 0 unless SRP_NG_CUSTOM is used for ng_type */
struct SRPUser *srp_user_new(SRP_HashAlgorithm alg, SRP_NGType ng_type,
const char *username, const char *username_for_verifier,
const unsigned char *bytes_password, size_t len_password, const char *n_hex,
const char *g_hex);
void srp_user_delete(struct SRPUser *usr);
int srp_user_is_authenticated(struct SRPUser *usr);
const char *srp_user_get_username(struct SRPUser *usr);
/* key_length may be null */
const unsigned char *srp_user_get_session_key(struct SRPUser *usr, size_t *key_length);
size_t srp_user_get_session_key_length(struct SRPUser *usr);
// clang-format off
/* Output: username, bytes_A, len_A.
* If you don't want it get written, set username to NULL.
* If bytes_a == NULL, random data is used for a. */
SRP_Result srp_user_start_authentication(struct SRPUser* usr, char **username,
const unsigned char *bytes_a, size_t len_a,
unsigned char **bytes_A, size_t* len_A);
/* Output: bytes_M, len_M (len_M may be null and will always be
* srp_user_get_session_key_length() bytes in size) */
void srp_user_process_challenge(struct SRPUser *usr,
const unsigned char *bytes_s, size_t len_s,
const unsigned char *bytes_B, size_t len_B,
unsigned char **bytes_M, size_t *len_M);
// clang-format on
/* bytes_HAMK must be exactly srp_user_get_session_key_length() bytes in size */
void srp_user_verify_session(struct SRPUser *usr, const unsigned char *bytes_HAMK);
#endif /* Include Guard */