OpenSSL EVP_DecryptFinal_ex解密失败问题求助

我尝试用OpenSSL实现AES-ECB模式的加解密，所有初始化步骤都返回成功，但最终调用EVP_DecryptFinal_ex时解密失败。已确认输入和密钥长度均能被16整除，参考过相关Stack Overflow线程及OpenSSL官方手册，试过同类问题的解决方案仍未解决，该函数返回0表示解密失败，无法定位具体原因。

代码实现 #

#include <stdio.h>
#include <string.h>
#include <stdbool.h>
#include <stdlib.h>

#include <openssl/conf.h>
#include <openssl/evp.h>
#include <openssl/err.h>

const char b64chars[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

int b64invs[] = { 62, -1, -1, -1, 63, 52, 53, 54, 55, 56, 57, 58,
    59, 60, 61, -1, -1, -1, -1, -1, -1, -1, 0, 1, 2, 3, 4, 5,
    6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20,
    21, 22, 23, 24, 25, -1, -1, -1, -1, -1, -1, 26, 27, 28,
    29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42,
    43, 44, 45, 46, 47, 48, 49, 50, 51 };

int b64_decode(const char *bytes, unsigned char *out, size_t *outlen) {
    size_t len;
    size_t i;
    size_t j;
    int    v;

    if (bytes == NULL)
        return 1;

    len = strlen(bytes);
    size_t b64_decoded_size = 9;
    
    b64_decoded_size = len / 4 * 3;

    for (i=len; i-->0; ) {
        if (bytes[i] == '=') {
            b64_decoded_size--;
        } else {
            break;
        }
    }

    if (*outlen < b64_decoded_size || len % 4 != 0 || out == NULL) {
        *outlen = b64_decoded_size;
        return 2;
    } else {
        *outlen = b64_decoded_size;
    }
        

    for (i=0; i<len; i++) {
        bool invalid_char = true;
        if (bytes[i] >= '0' && bytes[i] <= '9')
            invalid_char = false;
        else if (bytes[i] >= 'A' && bytes[i] <= 'Z')
            invalid_char = false;
        else if (bytes[i] >= 'a' && bytes[i] <= 'z')
            invalid_char = false;
        else if (bytes[i] == '+' || bytes[i] == '/' || bytes[i] == '=')
            invalid_char = false;

        if (invalid_char == true)
            return 3;
    }

    for (i=0, j=0; i<len; i+=4, j+=3) {
        v = b64invs[bytes[i]-43];
        v = (v << 6) | b64invs[bytes[i+1]-43];
        v = bytes[i+2]=='=' ? v << 6 : (v << 6) | b64invs[bytes[i+2]-43];
        v = bytes[i+3]=='=' ? v << 6 : (v << 6) | b64invs[bytes[i+3]-43];

        out[j] = (v >> 16) & 0xFF;
        if (bytes[i+2] != '=')
            out[j+1] = (v >> 8) & 0xFF;
        if (bytes[i+3] != '=')
            out[j+2] = v & 0xFF;
    }

    return 0;
}

int main () {    
    //Lyrics to yellow submarine, padded with spaces to make length 1200.
    unsigned char cipher_text[] = "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";
    unsigned char key[]         = "YELLOW SUBMARINE"; 
    size_t cipher_bytes_len  = 0;
    size_t cipher_text_len = strlen((const char *)cipher_text);

    b64_decode((const char *)cipher_text, NULL, &cipher_bytes_len);
    unsigned char cipher_bytes[cipher_bytes_len];
    b64_decode((const char *)cipher_text, cipher_bytes, &cipher_bytes_len);

    printf("cipher_text_len  = %ld\n", cipher_text_len);
    printf("cipher_bytes_len = %ld\n", cipher_bytes_len);
    
    EVP_CIPHER_CTX *ctx;
    int len;

    unsigned char plain[1584];

    if(!(ctx = EVP_CIPHER_CTX_new()))
        return 4;

    if(1 != EVP_DecryptInit_ex(ctx, EVP_aes_128_ecb(), NULL, key, NULL))
        return 5;

    if(1 != EVP_DecryptUpdate(ctx, plain, &len, cipher_text, cipher_text_len))
        return 6;
    
    int plain_len = len;
    printf("len = %d\n", len);
    printf("EVP_DecryptFinal_ex(ctx, plain + len, &len) = %d\n", EVP_DecryptFinal_ex(ctx, plain + plain_len, &len));

    EVP_CIPHER_CTX_free(ctx);

    return 0;
}

编译命令 #

gcc main.c -lcrypto

内容的提问来源于stack exchange，提问作者DavidT