解密（AES）和解码（Base64）后得到错误的纯文本

Question

我编写了一个小型测试程序，该程序使用纯文本字符串，使用AES对其进行加密，然后将其编码为base64。这部分看起来不错，但是当我尝试对数据进行解码和解密时，会得到错误的信息。

我的代码如下。 我对C还是很陌生，所以我想我是错误地在某个地方使用了指针或引用而犯了一个菜鸟错误。 我试图在EVP_DecryptFinal_ex函数中查找问题EVP_DecryptFinal_ex ，但似乎找不到错误。 注意！ 请忽略iv和key的使用，这只是测试代码。

码：

#define _GNU_SOURCE
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <math.h>
#include <openssl/evp.h>
#include <openssl/bio.h>
#include <openssl/pem.h>

// BASE 64 ENCODING
char* base64Encode(const unsigned char *message, const size_t length) {
    BIO *bio;
    BIO *b64;
    FILE* stream;

    int encodedSize = 4*ceil((double)length/3);
    char *buffer = (char*)malloc(encodedSize+1);

    stream = fmemopen(buffer, encodedSize+1, "w");
    b64 = BIO_new(BIO_f_base64());
    bio = BIO_new_fp(stream, BIO_NOCLOSE);
    bio = BIO_push(b64, bio);
    BIO_set_flags(bio, BIO_FLAGS_BASE64_NO_NL);
    BIO_write(bio, message, length);
    (void)BIO_flush(bio);
    BIO_free_all(bio);
    fclose(stream);

    return buffer;
}


// BASE 64 DECODING
int calcDecodeLength(const char *b64input) {
    int len = strlen(b64input);
    int padding = 0;

    // Check for trailing '=''s as padding
    if (b64input[len-1] == '=' && b64input[len-2] == '=') {
        padding = 2;
    } else if (b64input[len-1] == '=') {
        padding = 1;
    }
    return (int)len*0.75 - padding;
}

int base64Decode(const char *b64message, unsigned char **buffer) {
    BIO *bio;
    BIO *b64;
    int decodeLen = calcDecodeLength(b64message);

    *buffer = (unsigned char*)malloc(decodeLen+1);
    FILE* stream = fmemopen((char*)b64message, strlen(b64message), "r");

    b64 = BIO_new(BIO_f_base64());
    bio = BIO_new_fp(stream, BIO_NOCLOSE);
    bio = BIO_push(b64, bio);
    BIO_set_flags(bio, BIO_FLAGS_BASE64_NO_NL);
    size_t length = BIO_read(bio, *buffer, strlen(b64message));
    (*buffer)[length] = '\0';

    BIO_free_all(bio);
    fclose(stream);

    return decodeLen;
}


// AES ENCRYPTION
int encryptAes(const char *plainText, char *cipherText, const char *key) {
    unsigned char iv[] = { 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f };

    int plainTextLength = 0;
    int cipherTextLength = 0;
    int blockLength = 0;
    static const int MAX_PADDING_LENGTH = 16;

    EVP_CIPHER_CTX encryptCtx;
    EVP_CIPHER_CTX_init(&encryptCtx);

    plainTextLength = strlen(plainText);
    cipherText = (unsigned char *) malloc(plainTextLength + MAX_PADDING_LENGTH);

    // Initialise the encryption with AES256 (CBC mode) using the key and IV
    EVP_EncryptInit_ex(&encryptCtx, EVP_aes_256_cbc(), NULL, key, iv);

    // Encrypt the plainText into the cipherText, update cipherTextLength with the length of the generated cipherText
    if (!EVP_EncryptUpdate(&encryptCtx, cipherText, &blockLength, (unsigned char *) plainText, plainTextLength) ) {
        printf("Error in EVP_EncryptUpdate \n");
        return 1;
    }
    cipherTextLength += blockLength;

    // Encrypt the "final" data remaining in a partial block
    if (!EVP_EncryptFinal_ex(&encryptCtx, cipherText + cipherTextLength, &blockLength)) {
        printf("Error in EVP_EncryptFinal_ex \n");
        return 1;
    }
    cipherTextLength += blockLength;

    EVP_CIPHER_CTX_cleanup(&encryptCtx);
    return cipherTextLength;
}


// AES DECRYPTION
int decryptAes(const char *cipherText, char *decipheredPlainText, int cipherTextLength, const char *key) {
    unsigned char iv[] = { 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f };

    int plainTextLength = 0;
    int blockLength = 0;

    decipheredPlainText = (unsigned char *) malloc(cipherTextLength + 1);

    EVP_CIPHER_CTX decryptCtx;
    EVP_CIPHER_CTX_init(&decryptCtx);

    // Initialise the decryption with AES256 (CBC mode) using the key and IV
    EVP_DecryptInit_ex(&decryptCtx, EVP_aes_256_cbc(), NULL, key, iv);

    // Decrypt the cipherText into the plainText, update plainTextLength
    if (!EVP_DecryptUpdate(&decryptCtx, decipheredPlainText, &blockLength, cipherText, cipherTextLength)) {
        printf("Error in EVP_DecryptUpdate\n");
        return 1;
    }
    plainTextLength += blockLength;

    // Decrypt the "final" data remaining in a partial block
    if (!EVP_DecryptFinal_ex(&decryptCtx, decipheredPlainText + plainTextLength, &blockLength)) {
        printf("Error in EVP_DecryptFinal_ex\n");
        return 1;
    }
    plainTextLength += blockLength;

    EVP_CIPHER_CTX_cleanup(&decryptCtx);
    return plainTextLength;
}


int main(int argc, char **argv) {
    unsigned char key[] = { 0x2b, 0x7e, 0x15, 0x16, 0x28, 0xae, 0xd2, 0xa6, 0xab, 0xf7, 0x15, 0x88, 0x09, 0xcf, 0x4f, 0x3c };
    const char *plainText = "cipher cipher cipher cipher CIPHER TEXT! 187? 1$5 78@2 14 .TӒ��틪�ձ1z.$�?�U���<y";
    printf("Original Plain Text\t[%s]\n", plainText);

//////////////
// ENCRYPTION
//////////////
    // Encrypt the plain text using AES
    unsigned char cipherText[180];
    int cipherTextLength = encryptAes(plainText, cipherText, key);
    printf("Cipher Length\t\t[%d]\n", cipherTextLength);

    // Base64 encode the buffer
    char* encodedCipherText = base64Encode(cipherText, cipherTextLength);
    printf("Base64 is\t\t[%s]\n", encodedCipherText);

//////////////
// DECRYPTION
//////////////
    // Decode the Base64 string
    unsigned char* decodedCipherText;
    int decodedCipherTextLength = base64Decode(encodedCipherText, &decodedCipherText);
    printf("Decoded Cipher Length\t[%d]\n", decodedCipherTextLength);

    // Decrypt the cipher text
    unsigned char decryptedPlainText[180];
    int decryptedPlainTextLength = decryptAes(decodedCipherText, decryptedPlainText, decodedCipherTextLength, key);
    printf("Decrypted Plain Text\t[%s]\n", decryptedPlainText);

    // Compare before and after
    if (strcmp(plainText, (char *) decryptedPlainText) == 0) {
        printf("Decrypted data matches input data.\n");
    } else {
        printf("Decrypted data does not match input data.\n");
    }

    return 0;
}

命令：

gcc AesTest2.c -lcrypto -std=c99 -lm

输出：

Original Plain Text     [cipher cipher cipher cipher CIPHER TEXT! 187? 1$5 78@2 14 .TӒ��틪�ձ1z.$�?�U���<y]
Cipher Length           [112]
Base64 is               [AQAAAAAAAACIEYLbPgAAAOh04wX/fwAAdgAAAAAAAAAJAAAAAAAAAP504wX/fwAAAAAAAAAAAADgFILbPgAAABB14wX/fwAAlwWp2z4AAAAodeMF/38AAAAAAAABAAAA2LGg2z4AAABxB0AAAAAAAA==]
Decoded Cipher Length   [112]
Error in EVP_DecryptFinal_ex
Decrypted Plain Text    [�t��]
Decrypted data does not match input data.

经验丰富的C开发人员的任何帮助将不胜感激。 非常感谢。

Answer 1

您在main()声明缓冲区，并将对它们的引用向下传递给en / decrypt函数。

在这些en / decrypt函数中，您将用malloc()返回的结果覆盖从main()接收到的缓冲区地址。 然后将计算出的数据写入新分配的内存中。 从这两个加密/解密函数返回时，对后者的引用会丢失，从而导致内存泄漏。

由于所有这些， main()缓冲区根本没有被触及过。

通过在调用en / decrypt函数之前将它们设置为全0 ，并在从en / decrypt函数返回之后将它们打印出来，可以轻松证明这一点。