How to convert AES_encrypt in counter mode to EVP interfaces?

[URNOTCharlotte]

I previously used AES_encrypt to decrypt cipher text as follows:

     AES_set_encrypt_key(aeskey, 128, &aes_key);
     CRYPTO_ctr128_encrypt(encrypted_data,decrypted_data, sizeof(encrypted_data), &aes_key, aesiv, aes_ecount_buf, &aes_num, (block128_f) AES_encrypt);

After I upgrade the openssl lib to 3.0.12, and there are some warnings about "AES_set_encrypt_key" and "AES_encrypt". It seems that the standard is to to use EVP functions now with openssl.

Here is my code:

    OSSL_LIB_CTX *libctx = NULL;
    const char *propq = NULL;
    EVP_CIPHER_CTX *ctx;
    EVP_CIPHER *cipher = NULL;
    int decrypted_len = 0;
    unsigned char decrypted_data[encrypted_data_len];

     ctx = EVP_CIPHER_CTX_new();
     cipher = EVP_CIPHER_fetch(libctx, "AES-128-CTR", propq);
     EVP_CipherInit_ex2(ctx, cipher, aeskey, aesiv, AES_DECRYPT, NULL);
     EVP_CIPHER_CTX_set_padding(ctx, 0);
     EVP_CipherUpdate(ctx, decrypted_data, &decrypted_len, encrypted_data, encrypted_data_len);
     EVP_CipherFinal_ex(ctx, decrypted_data+decrypted_len, &decrypted_len);

But something is wrong with my implementations. I don't know how to set the "ecount_buf" with the EVP interfaces.
Any help appreciated. Thank you.

[slontis]

here is some code that works (this is just a copy of demos/ariacbc.c modified to do aes-ctr encrypt/decrypt on a KAT).

#include <stdio.h>
#include <openssl/err.h>
#include <openssl/bio.h>
#include <openssl/evp.h>
#include <openssl/crypto.h>
#include <openssl/core_names.h>

/* AES 128 bit key */
static const unsigned char ctr_key[] = {
    0xAE, 0x68, 0x52, 0xF8, 0x12, 0x10, 0x67, 0xCC,
    0x4B, 0xF7, 0xA5, 0x76, 0x55, 0x77, 0xF3, 0x9E
};

/* Unique initialisation vector */
static const unsigned char ctr_iv[] = {
    0x00, 0x00, 0x00, 0x30, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01
};

/* Example plaintext to encrypt */
static const unsigned char ctr_pt[] = {
    0x53, 0x69, 0x6E, 0x67, 0x6C, 0x65, 0x20, 0x62,
    0x6C, 0x6F, 0x63, 0x6B, 0x20, 0x6D, 0x73, 0x67
};

/* Expected ciphertext value */
static const unsigned char ctr_ct[] = {
    0xE4, 0x09, 0x5D, 0x4F, 0xB7, 0xA7, 0xB3, 0x79,
    0x2D, 0x61, 0x75, 0xA3, 0x26, 0x13, 0x11, 0xB8
};

/*
 * A library context and property query can be used to select & filter
 * algorithm implementations. If they are NULL then the default library
 * context and properties are used.
 */
OSSL_LIB_CTX *libctx = NULL;
const char *propq = NULL;

int aes_ctr_encrypt(void)
{
    int ret = 0;
    EVP_CIPHER_CTX *ctx;
    EVP_CIPHER *cipher = NULL;
    int outlen, tmplen;
    unsigned char outbuf[1024];

    printf("AES CTR Encrypt:\n");
    printf("Plaintext:\n");
    BIO_dump_fp(stdout, ctr_pt, sizeof(ctr_pt));

    /* Create a context for the encrypt operation */
    if ((ctx = EVP_CIPHER_CTX_new()) == NULL)
        goto err;

    /* Fetch the cipher implementation */
    if ((cipher = EVP_CIPHER_fetch(libctx, "AES-128-CTR", propq)) == NULL)
        goto err;

    /*
     * Initialise an encrypt operation with the cipher/mode, key and IV.
     * We are not setting any custom params so let params be just NULL.
     */
    if (!EVP_EncryptInit_ex2(ctx, cipher, ctr_key, ctr_iv, /* params */ NULL))
        goto err;

    /* Encrypt plaintext */
    if (!EVP_EncryptUpdate(ctx, outbuf, &outlen, ctr_pt, sizeof(ctr_pt)))
        goto err;

    /* Finalise: there can be some additional output from padding */
    if (!EVP_EncryptFinal_ex(ctx, outbuf + outlen, &tmplen))
        goto err;
    outlen += tmplen;

    /* Output encrypted block */
    printf("Ciphertext (outlen:%d):\n", outlen);
    BIO_dump_fp(stdout, outbuf, outlen);

    if (sizeof(ctr_ct) == outlen && !CRYPTO_memcmp(outbuf, ctr_ct, outlen))
        printf("Final ciphertext matches expected ciphertext\n");
    else
        printf("Final ciphertext differs from expected ciphertext\n");

    ret = 1;
err:
    if (!ret)
        ERR_print_errors_fp(stderr);

    EVP_CIPHER_free(cipher);
    EVP_CIPHER_CTX_free(ctx);

    return ret;
}

int aes_ctr_decrypt(void)
{
    int ret = 0;
    EVP_CIPHER_CTX *ctx;
    EVP_CIPHER *cipher = NULL;
    int outlen, tmplen;
    unsigned char outbuf[1024];

    printf("AES CTR Decrypt:\n");
    printf("Ciphertext:\n");
    BIO_dump_fp(stdout, ctr_ct, sizeof(ctr_ct));

    if ((ctx = EVP_CIPHER_CTX_new()) == NULL)
        goto err;

    /* Fetch the cipher implementation */
    if ((cipher = EVP_CIPHER_fetch(libctx, "AES-128-CTR", propq)) == NULL)
        goto err;

    /*
     * Initialise an encrypt operation with the cipher/mode, key and IV.
     * We are not setting any custom params so let params be just NULL.
     */
    if (!EVP_DecryptInit_ex2(ctx, cipher, ctr_key, ctr_iv, /* params */ NULL))
        goto err;

    /* Decrypt plaintext */
    if (!EVP_DecryptUpdate(ctx, outbuf, &outlen, ctr_ct, sizeof(ctr_ct)))
        goto err;

    /* Finalise: there can be some additional output from padding */
    if (!EVP_DecryptFinal_ex(ctx, outbuf + outlen, &tmplen))
        goto err;
    outlen += tmplen;

    /* Output decrypted block */
    printf("Plaintext (outlen:%d):\n", outlen);
    BIO_dump_fp(stdout, outbuf, outlen);

    if (sizeof(ctr_pt) == outlen && !CRYPTO_memcmp(outbuf, ctr_pt, outlen))
        printf("Final plaintext matches original plaintext\n");
    else
        printf("Final plaintext differs from original plaintext\n");

    ret = 1;
err:
    if (!ret)
        ERR_print_errors_fp(stderr);

    EVP_CIPHER_free(cipher);
    EVP_CIPHER_CTX_free(ctx);

    return ret;
}

int main(int argc, char **argv)
{
    if (!aes_ctr_encrypt())
        return EXIT_FAILURE;

    if (!aes_ctr_decrypt())
        return EXIT_FAILURE;

    return EXIT_SUCCESS;
}

[slontis]

Perhaps your inputs are not the right size?

[URNOTCharlotte]

Thank you very much for your reply. But I try to use the old APIs like this, it works:

 AES_set_encrypt_key(aeskey, 128, &aes_key);
 CRYPTO_ctr128_encrypt(encrypted_data,decrypted_data, sizeof(encrypted_data), &aes_key, aesiv, aes_ecount_buf, &aes_num, (block128_f) AES_encrypt);

In your code, I could not find something like "aes_ecount_buf" and "aes_num". Are these no longer supported by the EVP interfaces?

[kroeckx]

As far as I understand, aes_ecount_buf and num are state that you needed to keep, but the EVP interface keeps for you.