demos/evp/aesgcm.c

/*
 * Simple AES GCM test program, uses the same NIST data used for the FIPS
 * self test but uses the application level EVP APIs.
 */
#include <stdio.h>
#include <openssl/bio.h>
#include <openssl/evp.h>

/* AES-GCM test data from NIST public test vectors */

static const unsigned char gcm_key[] = {
    0xee, 0xbc, 0x1f, 0x57, 0x48, 0x7f, 0x51, 0x92, 0x1c, 0x04, 0x65, 0x66,
    0x5f, 0x8a, 0xe6, 0xd1, 0x65, 0x8b, 0xb2, 0x6d, 0xe6, 0xf8, 0xa0, 0x69,
    0xa3, 0x52, 0x02, 0x93, 0xa5, 0x72, 0x07, 0x8f
};

static const unsigned char gcm_iv[] = {
    0x99, 0xaa, 0x3e, 0x68, 0xed, 0x81, 0x73, 0xa0, 0xee, 0xd0, 0x66, 0x84
};

static const unsigned char gcm_pt[] = {
    0xf5, 0x6e, 0x87, 0x05, 0x5b, 0xc3, 0x2d, 0x0e, 0xeb, 0x31, 0xb2, 0xea,
    0xcc, 0x2b, 0xf2, 0xa5
};

static const unsigned char gcm_aad[] = {
    0x4d, 0x23, 0xc3, 0xce, 0xc3, 0x34, 0xb4, 0x9b, 0xdb, 0x37, 0x0c, 0x43,
    0x7f, 0xec, 0x78, 0xde
};

static const unsigned char gcm_ct[] = {
    0xf7, 0x26, 0x44, 0x13, 0xa8, 0x4c, 0x0e, 0x7c, 0xd5, 0x36, 0x86, 0x7e,
    0xb9, 0xf2, 0x17, 0x36
};

static const unsigned char gcm_tag[] = {
    0x67, 0xba, 0x05, 0x10, 0x26, 0x2a, 0xe4, 0x87, 0xd7, 0x37, 0xee, 0x62,
    0x98, 0xf7, 0x7e, 0x0c
};

void aes_gcm_encrypt(void)
{
    EVP_CIPHER_CTX *ctx;
    int outlen, tmplen;
    unsigned char outbuf[1024];
    printf("AES GCM Encrypt:\n");
    printf("Plaintext:\n");
    BIO_dump_fp(stdout, gcm_pt, sizeof(gcm_pt));
    ctx = EVP_CIPHER_CTX_new();
    /* Set cipher type and mode */
    EVP_EncryptInit_ex(ctx, EVP_aes_256_gcm(), NULL, NULL, NULL);
    /* Set IV length if default 96 bits is not appropriate */
    EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IVLEN, sizeof(gcm_iv), NULL);
    /* Initialise key and IV */
    EVP_EncryptInit_ex(ctx, NULL, NULL, gcm_key, gcm_iv);
    /* Zero or more calls to specify any AAD */
    EVP_EncryptUpdate(ctx, NULL, &outlen, gcm_aad, sizeof(gcm_aad));
    /* Encrypt plaintext */
    EVP_EncryptUpdate(ctx, outbuf, &outlen, gcm_pt, sizeof(gcm_pt));
    /* Output encrypted block */
    printf("Ciphertext:\n");
    BIO_dump_fp(stdout, outbuf, outlen);
    /* Finalise: note get no output for GCM */
    EVP_EncryptFinal_ex(ctx, outbuf, &outlen);
    /* Get tag */
    EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_GET_TAG, 16, outbuf);
    /* Output tag */
    printf("Tag:\n");
    BIO_dump_fp(stdout, outbuf, 16);
    EVP_CIPHER_CTX_free(ctx);
}

void aes_gcm_decrypt(void)
{
    EVP_CIPHER_CTX *ctx;
    int outlen, tmplen, rv;
    unsigned char outbuf[1024];
    printf("AES GCM Derypt:\n");
    printf("Ciphertext:\n");
    BIO_dump_fp(stdout, gcm_ct, sizeof(gcm_ct));
    ctx = EVP_CIPHER_CTX_new();
    /* Select cipher */
    EVP_DecryptInit_ex(ctx, EVP_aes_256_gcm(), NULL, NULL, NULL);
    /* Set IV length, omit for 96 bits */
    EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IVLEN, sizeof(gcm_iv), NULL);
    /* Specify key and IV */
    EVP_DecryptInit_ex(ctx, NULL, NULL, gcm_key, gcm_iv);
#if 0
    /*
     * Set expected tag value. A restriction in OpenSSL 1.0.1c and earlier
     * required the tag before any AAD or ciphertext
     */
    EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_TAG, sizeof(gcm_tag), gcm_tag);
#endif
    /* Zero or more calls to specify any AAD */
    EVP_DecryptUpdate(ctx, NULL, &outlen, gcm_aad, sizeof(gcm_aad));
    /* Decrypt plaintext */
    EVP_DecryptUpdate(ctx, outbuf, &outlen, gcm_ct, sizeof(gcm_ct));
    /* Output decrypted block */
    printf("Plaintext:\n");
    BIO_dump_fp(stdout, outbuf, outlen);
    /* Set expected tag value. Works in OpenSSL 1.0.1d and later */
    EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_TAG, sizeof(gcm_tag), gcm_tag);
    /* Finalise: note get no output for GCM */
    rv = EVP_DecryptFinal_ex(ctx, outbuf, &outlen);
    /*
     * Print out return value. If this is not successful authentication
     * failed and plaintext is not trustworthy.
     */
    printf("Tag Verify %s\n", rv > 0 ? "Successful!" : "Failed!");
    EVP_CIPHER_CTX_free(ctx);
}

int main(int argc, char **argv)
{
    aes_gcm_encrypt();
    aes_gcm_decrypt();
}