加解密：基於 openssl 實現 des ede3 cbc pkcs#5 算法

加解密：基於 openssl 實現 des ede3 cbc pkcs#5 算法

Code：

#include <stdio.h>
#include <stdlib.h>
#include <openssl/evp.h>
#include <openssl/x509.h>

void encrypt_des_ede_cbc_pkcs(
	unsigned char *in,		// 待加密數據
	unsigned int   inLen,	// 待加密數據字節數
	unsigned char *key,		// 密  鑰，長度總是24字節
	unsigned char *iv)		// 偏移量，長度總是08字節
{
	printf("encrypt......\n\n");

	unsigned char *outBuf;
	unsigned int outBufLen, outLen1, outLen2;

	/* 依據PKCS填充規則 */
	outBufLen = (inLen/8 + 1) * 8;
	outBuf = (unsigned char *)malloc(outBufLen);

	EVP_CIPHER_CTX ctx;
	EVP_CIPHER_CTX_init(&ctx);
	EVP_EncryptInit_ex(&ctx, EVP_des_ede3_cbc(), NULL, key, iv);
	EVP_EncryptUpdate(&ctx, outBuf, &outLen1, in, inLen);
	EVP_EncryptFinal_ex(&ctx, outBuf+outLen1, &outLen2);

	unsigned int i;
	for (i = 0; i < outBufLen; i++)
	{
		printf("%02x ", outBuf[i]);
	}
	printf("\n");

	free(outBuf);

	printf("in: %p\n", in);
	printf("inLen: %u\n", inLen);
	printf("outBufLen: %u\n", outBufLen);
	printf("outLen1: %u\n", outLen1);
	printf("outLen2: %u\n", outLen2);
	printf("\n\n");
}

void decrypt_des_ede_cbc_pkcs(
	unsigned char *out,		// 待解密數據
	unsigned int   outLen,	// 待解密數據字節數
	unsigned char *key,		// 密  鑰，長度總是24字節
	unsigned char *iv)		// 偏移量，長度總是08字節
{
	printf("decrypt......\n\n");

	unsigned char *inBuf;
	unsigned int inBufLen, inLen1, inLen2;

	/* 依據PKCS填充規則 */
	inBufLen = (outLen/8 - 1) * 8;
	inBuf = (unsigned char *)malloc(inBufLen);

	EVP_CIPHER_CTX ctx;
	EVP_CIPHER_CTX_init(&ctx);
	EVP_DecryptInit_ex(&ctx, EVP_des_ede3_cbc(), NULL, key, iv);
	EVP_DecryptUpdate(&ctx, inBuf, &inLen1, out, outLen);
	EVP_DecryptFinal_ex(&ctx, inBuf+inLen1, &inLen2);

	unsigned int i;
	for (i = 0; i < inBufLen; i++)
	{
		printf("%02x ", inBuf[i]);
	}
	printf("\n");

	free(inBuf);

	printf("out: %p\n", out);
	printf("outLen: %u\n", outLen);
	printf("inBufLen: %u\n", inBufLen);
	printf("inLen1: %u\n", inLen1);
	printf("inLen2: %u\n", inLen2);
	printf("\n\n");
}

int main()
{
	/* 加載算法 */
	OpenSSL_add_all_algorithms();

	/* 密鑰長度24字節 */
	unsigned char key[]	= { 0x12, 0x34, 0x56, 0x78, 0x90, 0xab, 0xcd, 0xef,
							0x12, 0x34, 0x56, 0x78, 0x90, 0xab, 0xcd, 0xef,
							0x12, 0x34, 0x56, 0x78, 0x90, 0xab, 0xcd, 0xef };

	/* 偏移量長度8字節 */
	unsigned char iv []	= { 0x12, 0x34, 0x56, 0x78, 0x90, 0xab, 0xcd, 0xef };

	/* 加密 */
	unsigned char in [] = "test1280";
	unsigned int  inLen = 8; // 不可strlen(in)，考慮到in中包含0x00字節會導致獲取待加密數據長度錯誤
	encrypt_des_ede_cbc_pkcs(in, inLen, key, iv);

	/* 解密 */
	unsigned char out[] = {	0x64, 0x5a, 0x6b, 0xd6, 0xbf, 0xf8, 0x36, 0xb2,
							0x4f, 0xd1, 0x74, 0xf6, 0xe7, 0xf6, 0xaf, 0xdb };
	unsigned int outLen = 16;// 不可strlen(out)
	decrypt_des_ede_cbc_pkcs(out, outLen, key, iv);

	return 0;
}

編譯 & 運行：

$ gcc -o main main.c -lssl -lcrypto
$ ./main
encrypt......

64 5a 6b d6 bf f8 36 b2 4f d1 74 f6 e7 f6 af db 
in: 0x7fff77a7c910
inLen: 8
outBufLen: 16
outLen1: 8
outLen2: 8


decrypt......

74 65 73 74 31 32 38 30 
out: 0x7fff77a7c900
outLen: 16
inBufLen: 8
inLen1: 8
inLen2: 0

注意：

代碼中沒有特別指明使用什麼填充算法，但實際上默認使用了pkcs#5填充算法：

man EVP_des_ede3_cbc 或者：
https://www.openssl.org/docs/man1.0.2/man3/EVP_des_ede3_cbc.html 有說：

If padding is enabled (the default) then EVP_EncryptFinal_ex() encrypts the “final” data, that is any data that remains in a partial block. It uses standard block padding (aka PKCS padding).

If padding is disabled then EVP_EncryptFinal_ex() will not encrypt any more data and it will return an error if any data remains in a partial block: that is if the total data length is not a multiple of the block size.

因此，默認情況下，EVP_EncryptFinal_ex() 使用PKCS#5填充。

PKCS說明：

PKCS padding works by adding n padding bytes of value n to make the total length of the encrypted data a multiple of the block size. Padding is always added so if the data is already a multiple of the block size n will equal the block size. For example if the block size is 8 and 11 bytes are to be encrypted then 5 padding bytes of value 5 will be added.

等價的，基於 java 實現 des ede3 cbc pkcs#5 算法，請參見：

https://blog.csdn.net/test1280/article/details/105255023

參考：

1.https://www.openssl.org/docs/man1.0.2/man3/EVP_des_ede3_cbc.html
2.https://www.openssl.org/docs/man1.0.2/man3/EVP_des_ede3_cbc.html#NOTES
3.https://blog.csdn.net/lrhui0903/article/details/39781623
4.https://stackoverflow.com/questions/9038298/java-desede-encrypt-openssl-equivalent
5.https://www.cnblogs.com/AloneSword/p/3479429.html