This is a fork of the mbed port of axTLS

Dependents:   TLS_axTLS-Example HTTPSClientExample

Overview

This library is a fork from the mbed port of axTLS. It attempts to :

  • reduce the usage of dynamic memory
  • verify certificates with key size up to 2048 bits
  • provide a simple interface

Encryption

This library uses either RC4 or AES for encryption.

Memory usage

During the establishment of a connection, about 10KB of memory is allocated dynamically (it depends on certificates). Once the connection is established, the memory consumption is relatively low. This means that your program must not use too much static memory or allocate memory before you establish a TLS connection.

Certificates

Certificates are the major source of problem and will often be the reason why your program will crash. Due to memory constraint, there are some limitations on certificates :

  • Each certificate must not be bigger than 2KB
  • TLS client can only handle a chain of up to three certificates (excluding the root certificate). This means that the server must not send more than three certificates.

Also, this library can only load certificates following these specifications :

  • encoded in binary DER format (PKCS1)
  • The public key must use RSA only

Once the connection is established, you should free all loaded certificates by calling CertificateManager::clear(). This will free a few kilobytes (it depends on your certificates). In addition, to enable certificate verification during the connection, this library has a "precomputed mode". This mode uses much less memory than a normal certificate verification.

Normal mode

You need to copy the root certificate in binary-DER format on the mbed. Then in your code, let's say that your root certificate is saved on the mbed as "root.der", assuming that you include CertificateManager.h and that you created a LocalFileSystem, you can load this certificate as this ;

Load root certificate

CertificateManager::add("/local/root.der");
CertificateManager::load();

Do not forget that this mode takes quite a lot of memory ( the memory peak is high while verifying certificates) and will only work if the key size is not bigger than 1024 bits (otherwise it will crash while verifying certificates).

Precomputed mode

In this mode, you need to save the entire chain of certificates (in binary-DER format) including the root certificate on the mbed. In practice, this means that you must first retrieve all certificates that the server sends during a connection and then find the right root certificate. In your code, you must call CertificateManager::add for each certificate and in the right order : from the server certificate to the root certificate. Here is how you shoud load certificates in this mode :

Loadcertificates in precomputed mode

CertificateManager::add("/local/server1.der");
CertificateManager::add("/local/server2.der");
CertificateManager::add("/local/server3.der");
CertificateManager::add("/local/root.der");
CertificateManager::load(true);

Using this mode, you should be able to verify certificates with key size up to 2048 bits.

How do I find these certificates ?

I posted an entry in my notebook detailing how to get certificates from a server. You should be able to get all certificates you need except the root certificate. Here is a way how to get the root certificate on windows :

  1. Open (double-click) the last certificate sent by the server
  2. Go to details panel and click on the entry called Issuer. The first line gives you the name of this certificate and the second line indicates the company who created this certificate
  3. Open firefox
  4. Go to options, advanced panel and click on View Certificates
  5. Go to Authorities panel
  6. Choose the certificate whose name match the issuer of the last certificate sent by the server
  7. Export this certificate to binary-DER format.

Connect to mbed.org !

Import programTLS_axTLS-Example

Establishing a connection to mbed.org using TLS

axTLS/crypto/crypto.h

Committer:
feb11
Date:
2013-09-12
Revision:
0:85fceccc1a7c

File content as of revision 0:85fceccc1a7c:

/*
 * Copyright (c) 2007, Cameron Rich
 * 
 * All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without 
 * modification, are permitted provided that the following conditions are met:
 *
 * * Redistributions of source code must retain the above copyright notice, 
 *   this list of conditions and the following disclaimer.
 * * Redistributions in binary form must reproduce the above copyright notice, 
 *   this list of conditions and the following disclaimer in the documentation 
 *   and/or other materials provided with the distribution.
 * * Neither the name of the axTLS project nor the names of its contributors 
 *   may be used to endorse or promote products derived from this software 
 *   without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/**
 * @file crypto.h
 */

#ifndef HEADER_CRYPTO_H
#define HEADER_CRYPTO_H

#ifdef __cplusplus
extern "C" {
#endif

#include "bigint_impl.h"
#include "bigint.h"

#ifndef STDCALL
#define STDCALL
#endif
#ifndef EXP_FUNC
#define EXP_FUNC
#endif


/* enable features based on a 'super-set' capbaility. */
#if defined(CONFIG_SSL_FULL_MODE) 

#ifndef CONFIG_SSL_ENABLE_CLIENT
#define CONFIG_SSL_ENABLE_CLIENT
#endif

#ifndef CONFIG_SSL_CERT_VERIFICATION
#define CONFIG_SSL_CERT_VERIFICATION
#endif

#elif defined(CONFIG_SSL_ENABLE_CLIENT) && !defined(CONFIG_SSL_CERT_VERIFICATION)
#define CONFIG_SSL_CERT_VERIFICATION
#endif

/**************************************************************************
 * AES declarations 
 **************************************************************************/

#define AES_MAXROUNDS            14
#define AES_BLOCKSIZE           16
#define AES_IV_SIZE             16

typedef struct aes_key_st 
{
    uint16_t rounds;
    uint16_t key_size;
    uint32_t ks[(AES_MAXROUNDS+1)*8];
    uint8_t iv[AES_IV_SIZE];
} AES_CTX;

typedef enum
{
    AES_MODE_128,
    AES_MODE_256
} AES_MODE;

void AES_set_key(AES_CTX *ctx, const uint8_t *key, 
        const uint8_t *iv, AES_MODE mode);
void AES_cbc_encrypt(AES_CTX *ctx, const uint8_t *msg, 
        uint8_t *out, int length);
void AES_cbc_decrypt(AES_CTX *ks, const uint8_t *in, uint8_t *out, int length);
void AES_convert_key(AES_CTX *ctx);

/**************************************************************************
 * RC4 declarations 
 **************************************************************************/

typedef struct 
{
    uint8_t x, y, m[256];
} RC4_CTX;

void RC4_setup(RC4_CTX *s, const uint8_t *key, int length);
void RC4_crypt(RC4_CTX *s, const uint8_t *msg, uint8_t *data, int length);

/**************************************************************************
 * SHA1 declarations 
 **************************************************************************/

#define SHA1_SIZE   20

/*
 *  This structure will hold context information for the SHA-1
 *  hashing operation
 */
typedef struct 
{
    uint32_t Intermediate_Hash[SHA1_SIZE/4]; /* Message Digest */
    uint32_t Length_Low;            /* Message length in bits */
    uint32_t Length_High;           /* Message length in bits */
    uint16_t Message_Block_Index;   /* Index into message block array   */
    uint8_t Message_Block[64];      /* 512-bit message blocks */
} SHA1_CTX;

void SHA1_Init(SHA1_CTX *);
void SHA1_Update(SHA1_CTX *, const uint8_t * msg, int len);
void SHA1_Final(uint8_t *digest, SHA1_CTX *);

/**************************************************************************
 * MD2 declarations 
 **************************************************************************/

#define MD2_SIZE 16

typedef struct
{
    unsigned char cksum[16];    /* checksum of the data block */
    unsigned char state[48];    /* intermediate digest state */
    unsigned char buffer[16];   /* data block being processed */
    int left;                   /* amount of data in buffer */
} MD2_CTX;

EXP_FUNC void STDCALL MD2_Init(MD2_CTX *ctx);
EXP_FUNC void STDCALL MD2_Update(MD2_CTX *ctx, const uint8_t *input, int ilen);
EXP_FUNC void STDCALL MD2_Final(uint8_t *digest, MD2_CTX *ctx);

/**************************************************************************
 * MD5 declarations 
 **************************************************************************/

#define MD5_SIZE    16
#define MAX_KEYBLOCK_SIZE 136
typedef struct 
{
  uint32_t state[4];        /* state (ABCD) */
  uint32_t count[2];        /* number of bits, modulo 2^64 (lsb first) */
  uint8_t buffer[64];       /* input buffer */
} MD5_CTX;

EXP_FUNC void STDCALL MD5_Init(MD5_CTX *);
EXP_FUNC void STDCALL MD5_Update(MD5_CTX *, const uint8_t *msg, int len);
EXP_FUNC void STDCALL MD5_Final(uint8_t *digest, MD5_CTX *);

/**************************************************************************
 * HMAC declarations 
 **************************************************************************/
void hmac_md5(const uint8_t *msg, int length, const uint8_t *key, 
        int key_len, uint8_t *digest);
void hmac_sha1(const uint8_t *msg, int length, const uint8_t *key, 
        int key_len, uint8_t *digest);

/**************************************************************************
 * RSA declarations 
 **************************************************************************/

typedef struct 
{
    bigint *m;              /* modulus */
    bigint *e;              /* public exponent */
    bigint *d;              /* private exponent */
#ifdef CONFIG_BIGINT_CRT
    bigint *p;              /* p as in m = pq */
    bigint *q;              /* q as in m = pq */
    bigint *dP;             /* d mod (p-1) */
    bigint *dQ;             /* d mod (q-1) */
    bigint *qInv;           /* q^-1 mod p */
#endif
    int num_octets;
    BI_CTX *bi_ctx;
} RSA_CTX;

void RSA_priv_key_new(RSA_CTX **rsa_ctx, 
        const uint8_t *modulus, int mod_len,
        const uint8_t *pub_exp, int pub_len,
        const uint8_t *priv_exp, int priv_len
#ifdef CONFIG_BIGINT_CRT
      , const uint8_t *p, int p_len,
        const uint8_t *q, int q_len,
        const uint8_t *dP, int dP_len,
        const uint8_t *dQ, int dQ_len,
        const uint8_t *qInv, int qInv_len
#endif
        );
void RSA_pub_key_new(RSA_CTX **rsa_ctx, 
        const uint8_t *modulus, int mod_len,
        const uint8_t *pub_exp, int pub_len);
void RSA_free(RSA_CTX *ctx);
int RSA_decrypt(const RSA_CTX *ctx, const uint8_t *in_data, uint8_t *out_data,
        int is_decryption);
bigint *RSA_private(const RSA_CTX *c, bigint *bi_msg);
//#if defined(CONFIG_SSL_CERT_VERIFICATION) || defined(CONFIG_SSL_GENERATE_X509_CERT)
bigint *RSA_sign_verify(BI_CTX *ctx, const uint8_t *sig, int sig_len,
        bigint *modulus, bigint *pub_exp);
bigint *RSA_public(const RSA_CTX * c, bigint *bi_msg);
int RSA_encrypt(const RSA_CTX *ctx, const uint8_t *in_data, uint16_t in_len, 
        uint8_t *out_data, int is_signing);
void RSA_print(const RSA_CTX *ctx);
//#endif

/**************************************************************************
 * RNG declarations 
 **************************************************************************/
EXP_FUNC void STDCALL RNG_initialize(void);
EXP_FUNC void STDCALL RNG_custom_init(const uint8_t *seed_buf, int size);
EXP_FUNC void STDCALL RNG_terminate(void);
EXP_FUNC void STDCALL get_random(int num_rand_bytes, uint8_t *rand_data);
void get_random_NZ(int num_rand_bytes, uint8_t *rand_data);

#ifdef __cplusplus
}
#endif

#endif