[openssl-users] One question about RSA decrypt with private key

[Yu Wei]

After commented out the line "EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_NO_PADDING)",  it worked well.


However, I still quite understand the usage of "RSA_NO_PADDING".


Who could kindly explain this?


Thanks,

Jared, (韦煜）
Software developer
Interested in open source software, big data, Linux

________________________________
From: openssl-users <openssl-users-bounces at openssl.org> on behalf of Yu Wei <yu2003w at hotmail.com>
Sent: Thursday, March 23, 2017 1:20:42 AM
To: openssl-users at openssl.org
Subject: [openssl-users] One question about RSA decrypt with private key


Hi guys,


I generated RSA private key and public key as below,

openssl genpkey -algorithm RSA -out key.pem -pkeyopt rsa_keygen_bits:2048

openssl rsa -pubout -in pri.key -out pub.key


And encrypted text file as below,

openssl pkeyutl -encrypt -pubin -inkey ~/pub.key -in ~/1.txt -out ~/1e.txt


Then I wrote below program to decrypt the encryted file. However, it seemed that decrypt didn't work as  expected.


#include <openssl/evp.h>
#include <openssl/rsa.h>
#include <openssl/pem.h>
#include <openssl/err.h>
#include <openssl/conf.h>
#include <iostream>

using namespace std;

void
cleanup()
{
    EVP_cleanup();
    CRYPTO_cleanup_all_ex_data();
    ERR_free_strings();
}

int
main(int argc, char** argv)
{
    ERR_load_crypto_strings();
    OpenSSL_add_all_algorithms();
    OPENSSL_config(nullptr);

    cout<<"Initialize crypto library done"<<endl;

    EVP_PKEY * key = EVP_PKEY_new();
    if (key == nullptr) {
        cout<<"Failed to contruct new key"<<endl;
        return 1;
    }
    FILE * fpri = nullptr;
    fpri = fopen("/home/stack/pri.key", "r");
    if (fpri == nullptr) {
        cout<<"Failed to load private key"<<endl;
        return 1;
    }
    key = PEM_read_PrivateKey(fpri, &key, nullptr, nullptr);
    if (key == nullptr) {
        std::cout<<"Read private key failed"<<endl;
        return 1;
    }
cout<<"load private key successfully"<<endl;
    EVP_PKEY_CTX *ctx = nullptr;
    ctx = EVP_PKEY_CTX_new(key, nullptr);
    EVP_PKEY_decrypt_init(ctx);
    EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_NO_PADDING);

    size_t outlen = 0, inlen = 0;
    unsigned char * out = nullptr, * in = nullptr;

    char buf[1024];
    FILE * fe = nullptr;
    fe = fopen("/home/stack/1e.txt", "r");
    size_t len = fread(buf, 1, sizeof(buf),  fe);
    cout<<"data input length is "<<len<<endl;
    EVP_PKEY_decrypt(ctx, NULL, &outlen, in, inlen);
    cout<<"outlen is "<<outlen<<endl;

    out = (unsigned char*)OPENSSL_malloc(outlen);
    EVP_PKEY_decrypt(ctx, out, &outlen, in, inlen);
    cout<<"decrypted data "<<out<<endl;
    cleanup();

    return 0;

}


When executing the code, the result is as below,

[stack at agent ~]$ ./test
Initialize crypto library done
load private key successfully
data input length is 256
outlen is 256
decrypted data


Is there anything missed?


Thanks,

Jared, (韦煜）
Software developer
Interested in open source software, big data, Linux
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