how to encrypt and decrypt string with openssl?

Question

Trying to encrypt and decrypt strings with evp functions of openssl. I tried the following source code but I got unexpected results (garbege output).

What I am missing?

#include <stdio.h>
#include <unistd.h>

#if 1

#include <openssl/evp.h>

char *se_evp_encrypt(char *ssid, char *data, int inl, char *ret, int *rb) 
{
    int i, tmp, ol;
    EVP_CIPHER_CTX  evpctx;
    char key[EVP_MAX_KEY_LENGTH] = {0};
    char iv[EVP_MAX_IV_LENGTH] = {0};

    *ret = '\0';

    strncpy(key, ssid, EVP_MAX_KEY_LENGTH);
    strncpy(iv, ssid, EVP_MAX_IV_LENGTH);

    EVP_EncryptInit(&evpctx, EVP_bf_cbc(), key, iv);
    EVP_EncryptUpdate(&evpctx, ret, &ol, data, inl);
    *rb = ol;
    EVP_EncryptFinal(&evpctx, ret, &ol);
    return ret;
}

char *se_evp_decrypt(char *ssid, char *ct, int inl, char *pt)
{
    int ol;
    EVP_CIPHER_CTX  evpctx;
    char key[EVP_MAX_KEY_LENGTH] = {0};
    char iv[EVP_MAX_IV_LENGTH] = {0};
    char final[EVP_MAX_BLOCK_LENGTH];

    *pt = '\0';

    strncpy(key, ssid, EVP_MAX_KEY_LENGTH);
    strncpy(iv, ssid, EVP_MAX_IV_LENGTH);

    EVP_DecryptInit(&evpctx, EVP_bf_cbc(), key, iv);

    EVP_DecryptUpdate(&evpctx, pt, &ol, ct, inl);
    if (!ol) /* there's no block to decrypt */
    {
        return "";
    }
    pt[ol] = 0;
    EVP_DecryptFinal(&evpctx, final, &inl);
    return pt;
}


int main(int argc,  char *argv[])
{
    char str[] = "abcdef123456789";
    char buf[256] = "", buf2[256] = "";
    int i;

    se_evp_encrypt("anyssid", str, strlen(str), buf, &i);


    printf("Ciphertext is %d bytes.    %d\n", i, strlen(str));

    se_evp_decrypt("anyssid", buf, i, buf2);
    printf("Decrypted: >>%s<<\n", buf2);

}
#endif

MOHAMED · Accepted Answer · 2020-03-15 17:01:11Z

fixed the source code in this way

#include <stdio.h>
#include <unistd.h>

#if 1

#include <openssl/evp.h>

char *se_evp_encrypt(char *ssid, char *data, int inl, char *ret, int *rb) 
{
    int i, tmp, ol;
    EVP_CIPHER_CTX  evpctx = {0};
    char key[EVP_MAX_KEY_LENGTH] = {0};
    char iv[EVP_MAX_IV_LENGTH] = {0};

    *ret = '\0';

    strncpy(key, ssid, EVP_MAX_KEY_LENGTH);
    strncpy(iv, ssid, EVP_MAX_IV_LENGTH);

    EVP_EncryptInit(&evpctx, EVP_bf_cbc(), key, iv);
    EVP_EncryptUpdate(&evpctx, ret, &ol, data, inl);
    EVP_EncryptFinal(&evpctx, ret + ol, &tmp);
    *rb = ol + tmp;
    return ret;
}

char *se_evp_decrypt(char *ssid, char *ct, int inl, char *pt)
{
    int ol, tmp;
    EVP_CIPHER_CTX  evpctx;
    char key[EVP_MAX_KEY_LENGTH] = {0};
    char iv[EVP_MAX_IV_LENGTH] = {0};
    char final[EVP_MAX_BLOCK_LENGTH];

    *pt = '\0';

    strncpy(key, ssid, EVP_MAX_KEY_LENGTH);
    strncpy(iv, ssid, EVP_MAX_IV_LENGTH);

    EVP_DecryptInit(&evpctx, EVP_bf_cbc(), key, iv);

    EVP_DecryptUpdate(&evpctx, pt, &ol, ct, inl);
    EVP_DecryptFinal(&evpctx, pt+ol , &tmp);

    pt[ol+tmp] = 0;

    return pt;
}


int main(int argc,  char *argv[])
{
    char str[] = "abcdef123456789";
    char buf[256] = "", buf2[256] = "";
    int i;

    se_evp_encrypt("anyssid", str, strlen(str), buf, &i);


    printf("Ciphertext is %d bytes.    %d\n", i, strlen(str));

    se_evp_decrypt("anyssid", buf, i, buf2);
    printf("Decrypted: >>%s<<\n", buf2);

}
#endif

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