使用openssl进行AES 128 CTR 加密、解密

参考文章

https://blog.youkuaiyun.com/yasi_xi/article/details/13997337

对称加密如非对称加密

AES128-CTR方式，属于对称加密的一种。
这里有一篇讲解对称和非对称加密非常通俗易懂的文章：
https://segmentfault.com/a/1190000004461428

代码示例

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <openssl/evp.h>

void handleErrors(void)
{
    ERR_print_errors_fp(stderr);
    abort();
}

int encrypt(unsigned char *plaintext, int plaintext_len, unsigned char *key,
            unsigned char *iv, unsigned char *ciphertext)
{
    EVP_CIPHER_CTX *ctx;

    int len;

    int ciphertext_len;

    /* Create and initialise the context */
    if (!(ctx = EVP_CIPHER_CTX_new()))
        handleErrors();

    /* Initialise the encryption operation. IMPORTANT - ensure you use a key
     * and IV size appropriate for your cipher
     * In this example we are using 256 bit AES (i.e. a 256 bit key). The
     * IV size for *most* modes is the same as the block size. For AES this
     * is 128 bits */
    if (1 != EVP_EncryptInit_ex(ctx, EVP_aes_128_ctr(), NULL, key, iv))
        handleErrors();

    /* Provide the message to be encrypted, and obtain the encrypted output.
     * EVP_EncryptUpdate can be called multiple times if necessary
     */
    if (1 != EVP_EncryptUpdate(ctx, ciphertext, &len, plaintext, plaintext_len))
        handleErrors();
    ciphertext_len = len;

    /* Finalise the encryption. Further ciphertext bytes may be written at
     * this stage.
     */
    if (1 != EVP_EncryptFinal_ex(ctx, ciphertext + len, &len))
        handleErrors();
    ciphertext_len += len;

    /* Clean up */
    EVP_CIPHER_CTX_free(ctx);

    return ciphertext_len;
}

int decrypt(unsigned char *ciphertext, int ciphertext_len, unsigned char *key,
            unsigned char *iv, unsigned char *plaintext)
{
    EVP_CIPHER_CTX *ctx;

    int len;

    int plaintext_len;

    /* Create and initialise the context */
    if (!(ctx = EVP_CIPHER_CTX_new()))
        handleErrors();

    /* Initialise the decryption operation. IMPORTANT - ensure you use a key
     * and IV size appropriate for your cipher
     * In this example we are using 256 bit AES (i.e. a 256 bit key). The
     * IV size for *most* modes is the same as the block size. For AES this
     * is 128 bits */
    if (1 != EVP_DecryptInit_ex(ctx, EVP_aes_128_ctr(), NULL, key, iv))
        handleErrors();

    /* Provide the message to be decrypted, and obtain the plaintext output.
     * EVP_DecryptUpdate can be called multiple times if necessary
     */
    if (1 != EVP_DecryptUpdate(ctx, plaintext, &len, ciphertext, ciphertext_len))
        handleErrors();
    plaintext_len = len;

    /* Finalise the decryption. Further plaintext bytes may be written at
     * this stage.
     */
    if (1 != EVP_DecryptFinal_ex(ctx, plaintext + len, &len))
        handleErrors();
    plaintext_len += len;

    /* Clean up */
    EVP_CIPHER_CTX_free(ctx);

    return plaintext_len;
}

int main(int argc, char const *argv[])
{
    /* A 256 bit key */
    unsigned char *key = (unsigned char *)"01234567890123456789012345678901";

    /* A 128 bit IV */
    unsigned char *iv = (unsigned char *)"0123456789012345";

    /* Message to be encrypted */
    unsigned char *plaintext = "The quick brown fox jumps over the lazy dog";

    /* Buffer for ciphertext. Ensure the buffer is long enough for the
     * ciphertext which may be longer than the plaintext, dependant on the
     * algorithm and mode
     */
    unsigned char ciphertext[128];

    /* Buffer for the decrypted text */
    unsigned char decryptedtext[128];

    int decryptedtext_len, ciphertext_len;

    printf("Plaintext is:\n%s~\n", plaintext);

    /* Encrypt the plaintext */
    ciphertext_len = encrypt(plaintext, strlen(plaintext), key, iv,
                             ciphertext);

    /* Do something useful with the ciphertext here */
    printf("Ciphertext is %d bytes long:\n", ciphertext_len);
    BIO_dump_fp(stdout, ciphertext, ciphertext_len);

    /* Decrypt the ciphertext */
    decryptedtext_len = decrypt(ciphertext, ciphertext_len, key, iv,
                                decryptedtext);

    /* Add a NULL terminator. We are expecting printable text */
    decryptedtext[decryptedtext_len] = '\0';

    /* Show the decrypted text */
    printf("Decrypted text is:\n");
    printf("%s~\n", decryptedtext);

    return 0;
}

编译

gcc openssl-aes-128-ctr.c -lssl -lcrypto

运行效果

Plaintext is:
The quick brown fox jumps over the lazy dog~
Ciphertext is 43 bytes long:
0000 - 0b 15 95 9f 61 4f e5 29-8d da cf eb 69 db 55 0a   ....aO.)....i.U.
0010 - 00 58 58 fa 7c 6f d0 52-52 53 73 61 1b 08 2e 03   .XX.|o.RRSsa....
0020 - a2 d1 16 0c 98 4b f5 c7-43 6c ca                  .....K..Cl.
Decrypted text is:
The quick brown fox jumps over the lazy dog~