c语言中使用openssl对rsa私钥解密

单次加密数据的最大长度（block_len），由RSA秘钥模长RSA_size()和填充模式有关

  填充模式：RSA_PKCS1_PADDING， block_len=RSA_size() - 11填充模式：RSA_PKCS1_OAEP_PADDING，block_len=RSA_size() - 41填充模式：RSA_NO_PADDING（不填充），block_len=RSA_size()

本示例用RSA_PKCS1_PADDING填充，所以一次加密117字节，一次解密128字节，超过的字符需要循环解密。

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<openssl/rsa.h>
#include<openssl/pem.h>
#include<openssl/err.h>
#include<openssl/bio.h>
#include<openssl/evp.h>char* prikey="-----BEGIN RSA PRIVATE KEY-----\n\
MIICdwIBADANBgkqhkiG9w0BAQEFAASCAmEwggJdAgEAAoGB\
ALr1s+g6od9C0Jj/a+oEhSUGLOoM8QwAJlTkVTLeKrvEtZCP\
4AQRvsmH7akOo86ja2o33qK+p54AFoKr0T0GaQP6NfsklipK\
N0azBIiwo/tTlwOJUjW3fLQMMNRX/9ZtIYMGSPIOL4FdYJhT\
oJC/dPZ1khaJvf7Oi0rxPuMNVekZAgMBAAECgYBWi9smi83X\
TlTGHqdUA5enFf7AshD73y3fanvOOm5J0bvDGfc3qwdIv7XS\
5sYJqDjXSNm1ONDbIWtKPkN0Hn2J3wDMKzECvvlc+Jb9n1Sm\
7HblKI5PqB3578lcYUQ0M1fIa4AbUBPruInAkAOwuUWvfzmt\
gVky19BXDZNnS+UmAQJBAP389aYz/NfKMSvEq7zht8IQsqXA\
VQinoRLWGTg8uWTd6OZktuBxm9qQDSugIHQlS99PZrSL2xXf\
45bfYKWq7nkCQQC8cNJ+MBr787VmaHdaUK7K32S5NtgJ3g1O\
Nyuzuwi3fj/+PDxB2SMOSWMX5j10N2iGSQ9ctVpXlfaVtQPw\
LaehAkEAvyyU9enxqbct9aTOI5i+SNtqrGotVxtdmSD/0J2c\
ajjB4hDyudOpnQSKdUjMxL+B8W8Bfmo6mKdx1hEC3Q/g+QJB\
AKAlvi5yEazInQTwiWafJT3TBxYFTytrpKExcBmqPak8SYR2\
irtnn0xYADhiex3WrSVa2AxxL9s53ruygCtRkaECQCUkMs3i\
e2OUKa8MQBhup7cbhXiSunO354Xnc4ddjbgPLwW7tGoWEezi\
jNsiJ6XBSMcx6zifs1ybCbeDvdaT/Jo=\
\n-----END RSA PRIVATE KEY-----\n";typedef struct{unsigned char *data; //解密数据int len;            //解密数据长度
}decrypt_data_t;static void crypt_rsa_decrypt(unsigned char *endata,int enlen,decrypt_data_t *out_data){RSA *rsa;BIO *bio;if((bio = BIO_new_mem_buf(prikey, -1)) == NULL)       //从字符串读取RSA公钥{printf("BIO_new_mem_buf failed!\n");}if((rsa=PEM_read_bio_RSAPrivateKey(bio,NULL,NULL,NULL))==NULL){printf("PEM_read_bio_RSAPrivateKey failed!");}int key_len = RSA_size(rsa);int ret=0,pos=0;int blocklen = 128;out_data->data = (unsigned char *)malloc(enlen+1);memset(out_data->data,0,enlen+1);unsigned char *sub_str = (unsigned char *)malloc(key_len+1);unsigned char *out_str = (unsigned char *)malloc(key_len+1);memset(sub_str,0,key_len+1);memset(out_str,0,key_len+1);while(enlen-pos >0){if(enlen-pos >blocklen){memset(sub_str,0,key_len+1);memcpy(sub_str,endata+pos,blocklen);ret = RSA_private_decrypt(blocklen,(unsigned char *)sub_str,(unsigned char*)out_str,rsa,RSA_PKCS1_PADDING);printf("RSA_private_decrypt ret:%d\n",ret);pos +=blocklen;if(ret >0){								memcpy(out_data->data+out_data->len,out_str,ret);out_data->len += ret;}}else{				memset(sub_str,0,key_len+1);memcpy(sub_str,endata+pos,enlen-pos);ret = RSA_private_decrypt(enlen-pos,(unsigned char *)sub_str,(unsigned char*)out_str,rsa,RSA_PKCS1_PADDING);printf("RSA_private_decrypt ret:%d\n",ret);pos = enlen;if(ret >0){								memcpy(out_data->data+out_data->len,out_str,ret);out_data->len += ret;}		}}if(sub_str){free(sub_str);sub_str = NULL;}if(out_str){free(out_str);out_str = NULL;}RSA_free(rsa);BIO_free_all(bio);}