openssl_decrypt.c

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#include "crypto/openssl_decrypt.h"
 
#include <assert.h>                  // for assert
#include <stdint.h>                  // for uint32_t
#include <stdlib.h>                  // for calloc, free
#include <string.h>                  // for NULL, memcpy, size_t, strstr
 
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif // HAVE_CONFIG_H
 
#ifdef HAVE_WOLFSSL
#define OPENSSL_EXTRA
#define WC_NO_HARDEN
#include <wolfssl/options.h>
#include <wolfssl/openssl/aes.h>
#include <wolfssl/openssl/err.h>
#include <wolfssl/openssl/evp.h>
#else
#include <openssl/aes.h>
#include <openssl/err.h>
#include <openssl/evp.h>
#endif
 
#include "crypto/crc.h"
#include "crypto/md5.h"
#include "crypto/openssl_encrypt.h" // get_cipher
#include "debug.h"
#include "lib_common.h"
#include "utils/macros.h"            // for STR_LEN, snprintf_ch
 
#define GCM_TAG_LEN 16
#define MOD_NAME "[decrypt] "
 
struct openssl_decrypt {
        EVP_CIPHER_CTX *ctx;
        unsigned char key_hash[16];
 
        unsigned char ivec[AES_BLOCK_SIZE];
        unsigned char ecount[AES_BLOCK_SIZE];
        unsigned int num;
};
 
static int openssl_decrypt_init(struct openssl_decrypt **state,
                                const char *passphrase)
{
        struct openssl_decrypt *s =
                calloc(1, sizeof(struct openssl_decrypt));
 
        char pass[STR_LEN];
        snprintf_ch(pass, "%s", passphrase);
        // used only by encrypt, drop option
        if (strstr(pass, ":cipher=")) {
                 *strstr(pass, ":cipher=") = '\0';
        }
 
        MD5CTX context;
 
        MD5Init(&context);
        MD5Update(&context, (const unsigned char *) pass,
                        strlen(pass));
        MD5Final(s->key_hash, &context);
 
        s->ctx = EVP_CIPHER_CTX_new();
        log_msg(LOG_LEVEL_INFO, MOD_NAME "Enabled stream decryption.\n");
 
        *state = s;
        return 0;
}
 
static void openssl_decrypt_destroy(struct openssl_decrypt *s)
{
        if(!s) {
                return;
        }
        EVP_CIPHER_CTX_free(s->ctx);
        free(s);
}
 
#define CHECK(action, errmsg) do { int rc = action; if (rc != 1) { log_msg(LOG_LEVEL_ERROR, MOD_NAME errmsg ": %s\n", ERR_error_string(ERR_get_error(), NULL)); return 0; } } while(0)
#pragma GCC diagnostic ignored "-Wcast-qual"
static int openssl_decrypt(struct openssl_decrypt *decrypt,
                const char *ciphertext, int ciphertext_len,
                const char *aad, int aad_len,
                char *plaintext, enum openssl_mode mode)
{
        const EVP_CIPHER *cipher = get_cipher(mode);
        if (cipher == NULL) {
                log_msg(LOG_LEVEL_ERROR, MOD_NAME "Cipher %d not available!\n", (int) mode);
                return 0;
        }
        uint32_t data_len;
        memcpy(&data_len, ciphertext, sizeof(uint32_t));
        assert ((size_t) ciphertext_len >= data_len + sizeof(uint32_t) + 16 + sizeof(uint32_t));
        ciphertext += sizeof(uint32_t);
        const unsigned char *iv = (const unsigned char *) ciphertext;
        ciphertext += 16;
        ciphertext_len -= 20;
 
        CHECK(EVP_CipherInit(decrypt->ctx, cipher, decrypt->key_hash, iv, 0), "Unable to initialize cipher");
        CHECK(EVP_CIPHER_CTX_ctrl(decrypt->ctx, EVP_CTRL_GCM_SET_IVLEN, 16, NULL), "set IV len"); // default IV len is presumably 12 bytes
 
        int out_len = 0;
        if (mode == MODE_AES128_GCM) {
                ciphertext_len -= GCM_TAG_LEN;
                if (aad && aad_len > 0) {
                        if (!EVP_DecryptUpdate(decrypt->ctx, NULL, &out_len, (void *) aad, aad_len)) {
                                log_msg(LOG_LEVEL_ERROR, MOD_NAME "AAD processing: %s\n", ERR_error_string(ERR_get_error(), NULL));
                        }
                }
        }
        CHECK(EVP_CipherUpdate(decrypt->ctx, (unsigned char *) plaintext, &out_len, (const unsigned char *) ciphertext, ciphertext_len), "EVP_CipherUpdate");
        int total_len = out_len;
        if (mode == MODE_AES128_GCM) {
                CHECK(EVP_CIPHER_CTX_ctrl(decrypt->ctx, EVP_CTRL_GCM_SET_TAG, GCM_TAG_LEN, (void *) (ciphertext + ciphertext_len)), "GCM set tag");
        }
        CHECK(EVP_CipherFinal(decrypt->ctx, (unsigned char *) plaintext + out_len, &out_len), "EVP_CipherFinal");
        total_len += out_len;
 
        if (mode != MODE_AES128_GCM) {
                uint32_t expected_crc = 0;
                assert((size_t) total_len >= data_len + sizeof expected_crc);
                memcpy(&expected_crc, plaintext + data_len, sizeof expected_crc);
                uint32_t crc = crc32buf(aad, aad_len);
                crc = crc32buf_with_oldcrc(plaintext, data_len, crc);
                if (crc != expected_crc) {
                        log_msg(LOG_LEVEL_WARNING, MOD_NAME "Warning: Packet dropped AES - wrong CRC!\n");
                        return 0;
                }
        }
 
        return data_len;
}
 
static const struct openssl_decrypt_info functions = {
        openssl_decrypt_init,
        openssl_decrypt_destroy,
        openssl_decrypt,
};
 
REGISTER_MODULE(openssl_decrypt, &functions, LIBRARY_CLASS_UNDEFINED, OPENSSL_DECRYPT_ABI_VERSION);