用openssl库RSA加密解密

 #include <stdio.h>
 #include <openssl/rsa.h>
 #include <openssl/pem.h>
 #include <openssl/err.h>

 //加密
 int my_encrypt(const char *input, int input_len,  char *output, int *output_len, const char *pri_key_fn)
 {
         RSA  *p_rsa = NULL;
         FILE *file = NULL;
         int ret = ;

         if((file = fopen(pri_key_fn, "rb")) == NULL)
         {
                 ret = -;
                 goto End;
         }

         if((p_rsa = PEM_read_RSAPrivateKey(file, NULL,NULL,NULL )) == NULL)
         {
                 ret = -;
                 goto End;
         }

         if((*output_len = RSA_private_encrypt(input_len, (unsigned char*)input, (unsigned char*)output, p_rsa, RSA_PKCS1_PADDING)) < )
         {
                 ret = -;
                 goto End;
         }

 End:
         if(p_rsa != NULL)
                 RSA_free(p_rsa);
         if(file != NULL)
                 fclose(file);

         return ret;
 }

 //解密
 int my_decrypt(const char *input, int input_len,  char *output, int *output_len, const char *pri_key_fn)
 {
         RSA  *p_rsa = NULL;
         FILE *file = NULL;
         int ret = ;

         file = fopen(pri_key_fn, "rb");
         if(!file)
         {
                 ret = -;
                 goto End;
         }

         if((p_rsa = PEM_read_RSA_PUBKEY(file, NULL,NULL,NULL )) == NULL)
         {
                 ret = -;
                 goto End;
         }

         if((*output_len=RSA_public_decrypt(input_len, (unsigned char*)input, (unsigned char*)output, p_rsa, RSA_PKCS1_PADDING)) < )
         {
                 ret = -;
                 goto End;
         }
 End:
         if(p_rsa != NULL)
                 RSA_free(p_rsa);
         if(file != NULL)
                 fclose(file);

         return ret;
 }

 int main(int argc, char**argv)
 {
         char src[];
         char dst[];
         int src_len;
         int dst_len;
         int ret;
         FILE *f;

         src_len = fread(src, , , stdin);

         if(argv[][] == 'e') {
                 ret = my_encrypt(src, src_len,  dst, &dst_len, argv[]);
         }else {
                 ret = my_decrypt(src, src_len,  dst, &dst_len, argv[]);
         }

         if(ret) {
                 fprintf(stderr, "Error\n");
         }
         fwrite(dst,,dst_len,stdout);
         return ret;
 }

以上是一个示例，测试了私钥加密(签名)/公钥解密(验证)，main函数是一个测试

测试一下，先生成2048位公钥、私钥对

colin@colin-VirtualBox:/tmp$ openssl genrsa -out pri2048.pem
Generating RSA private key,  bit long modulus
................................+++
.............+++
e is  (0x10001)
colin@colin-VirtualBox:/tmp$ openssl rsa -in pri2048.pem -pubout -out pub2048.pem
writing RSA key

编译、文件测试

colin@colin-VirtualBox:/tmp$ gcc t.c -lssl -lcrypto -lm
colin@colin-VirtualBox:/tmp$ ./a.out en pri2048.pem <data >data.en
colin@colin-VirtualBox:/tmp$ ./a.out enc pri2048.pem <data >data.en
colin@colin-VirtualBox:/tmp$ ./a.out dec pub2048.pem <data.en >data2
colin@colin-VirtualBox:/tmp$ openssl rsautl -verify -in data.en -inkey pub2048.pem -pubin -out data3

对比一下

colin@colin-VirtualBox:/tmp$ cmp data data2
colin@colin-VirtualBox:/tmp$ cmp data data3
colin@colin-VirtualBox:/tmp$ md5sum data data2 data3
7a71146998ad521bab336a49f65c90c4  data
7a71146998ad521bab336a49f65c90c4  data2
7a71146998ad521bab336a49f65c90c4  data3

公钥加密、私钥解密就不写了，对着看就会很明白了。

int RSA_public_encrypt(int flen, const unsigned char *from,
unsigned char *to, RSA *rsa, int padding);
int RSA_private_encrypt(int flen, const unsigned char *from,
unsigned char *to, RSA *rsa, int padding);
int RSA_public_decrypt(int flen, const unsigned char *from,
unsigned char *to, RSA *rsa, int padding);
int RSA_private_decrypt(int flen, const unsigned char *from,
unsigned char *to, RSA *rsa, int padding);