Remove dirt in result of decrypt with openssl (C Language)

Question

After researching I think it's time to ask for some help because I can not understand where is the problem. I'm working with OpenSSL to encrypt and decrypt. I fixed the code to make it more clear who might be willing to help me. It basically consists of three functions: generate_key_pair, example_one, example_two In example one I load the contents of a file, cryptographer, put the contents in a variable, decrypt the contents of the variable putting the result in another variable. Everything works perfectly. In example two I carry the contents of a file, cryptographer, put the contents into a file, load the file contents, decrypt. In this case when I decrypt comes a "dirt" that I can not identify how to avoid. I put together these few words to the code, the command I'm using to compile and the result obtained. Already like to thank everyone.

COMPILE:

gcc -std=c99 source\RSA\RSA.c source\RSA\applink.c -Isource\RSA\include -Lsource\RSA\lib\openssl -leay32 -lssleay32 -o build\rsa.exe

CODE:

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

int generate_key_pair(int KEY_LENGTH, char *PRIVATE_KEY_FILENAME, char *PUBLIC_KEY_FILENAME)
{    
    FILE *KEY_FILE;
    RSA *KEY_PAIR;  
    int RESULT = 0;

    KEY_PAIR = RSA_generate_key(KEY_LENGTH, 17, NULL, NULL);    
    KEY_FILE = fopen(PRIVATE_KEY_FILENAME,"w");
    RESULT = PEM_write_RSAPrivateKey(KEY_FILE, KEY_PAIR, NULL, NULL, 0, NULL, NULL);
    fclose(KEY_FILE);
    KEY_FILE = fopen(PUBLIC_KEY_FILENAME,"w");
    RESULT = (RESULT && PEM_write_RSAPublicKey(KEY_FILE, KEY_PAIR));
    fclose(KEY_FILE);
    return RESULT;
}

void example_one(int KEY_LENGTH, char *PRIVATE_KEY_FILENAME, char *PUBLIC_KEY_FILENAME)
{   
    printf("--- EXAMPLE 1: BEGIN---\r\n\r\n");
    RSA *PUBLIC_KEY = NULL; 
    RSA *PRIVATE_KEY = NULL;
    FILE *KEY_FILE;

    KEY_FILE = fopen(PUBLIC_KEY_FILENAME, "r"); 
    PUBLIC_KEY = PEM_read_RSAPublicKey(KEY_FILE,NULL,NULL,NULL);

    KEY_FILE = fopen(PRIVATE_KEY_FILENAME, "r");    
    PRIVATE_KEY = PEM_read_RSAPrivateKey(KEY_FILE,NULL,NULL,NULL);

    int PUBLIC_KEY_SIZE = RSA_size(PUBLIC_KEY);
    int PRIVATE_KEY_SIZE = RSA_size(PRIVATE_KEY);

    FILE *INPUT_FILE = fopen("BUFFER.TXT", "r");        
    fseek(INPUT_FILE, 0, SEEK_END);
    int INPUT_FILE_SIZE = ftell(INPUT_FILE);
    rewind(INPUT_FILE);
    char *FILE_CONTENTS = malloc(KEY_LENGTH/8);
    fread(FILE_CONTENTS, sizeof(char), INPUT_FILE_SIZE, INPUT_FILE);
    fclose(INPUT_FILE);
    FILE_CONTENTS[INPUT_FILE_SIZE] = '\0';

    printf("ORIGINAL FILE_CONTENTS=\r\n%s\r\n\r\n",FILE_CONTENTS);

    char *ENCRYPTED = NULL;
    char *DECRYPTED = NULL;

    ENCRYPTED = malloc(PUBLIC_KEY_SIZE);
    RSA_public_encrypt(strlen(FILE_CONTENTS), (unsigned char*)FILE_CONTENTS, (unsigned char*)ENCRYPTED, PUBLIC_KEY, RSA_PKCS1_OAEP_PADDING);

    printf("ENCRYPTED=\r\n%s\r\n\r\n",ENCRYPTED);   

    DECRYPTED = malloc(PRIVATE_KEY_SIZE);
    RSA_private_decrypt(PRIVATE_KEY_SIZE, (unsigned char*)ENCRYPTED, (unsigned char*)DECRYPTED, PRIVATE_KEY, RSA_PKCS1_OAEP_PADDING);

    printf("DECRYPTED=\r\n%s\r\n\r\n",DECRYPTED);

    free(ENCRYPTED);
    ENCRYPTED = NULL;
    free(DECRYPTED);
    DECRYPTED = NULL;
    printf("--- EXAMPLE 1: END---\r\n\r\n");
}

void example_two(int KEY_LENGTH, char *PRIVATE_KEY_FILENAME, char *PUBLIC_KEY_FILENAME)
{
    printf("--- EXAMPLE 2: BEGIN---\r\n\r\n");
    RSA *PUBLIC_KEY = NULL; 
    RSA *PRIVATE_KEY = NULL;    
    FILE *KEY_FILE;

    KEY_FILE = fopen(PUBLIC_KEY_FILENAME, "r"); 
    PUBLIC_KEY = PEM_read_RSAPublicKey(KEY_FILE,NULL,NULL,NULL);

    KEY_FILE = fopen(PRIVATE_KEY_FILENAME, "r");    
    PRIVATE_KEY = PEM_read_RSAPrivateKey(KEY_FILE,NULL,NULL,NULL);

    int PUBLIC_KEY_SIZE = RSA_size(PUBLIC_KEY);
    int PRIVATE_KEY_SIZE = RSA_size(PRIVATE_KEY);

    FILE *INPUT_FILE = fopen("BUFFER.TXT", "r");        
    fseek(INPUT_FILE, 0, SEEK_END);
    int INPUT_FILE_SIZE = ftell(INPUT_FILE);
    rewind(INPUT_FILE);
    char *FILE_CONTENTS = malloc(KEY_LENGTH/8);
    fread(FILE_CONTENTS, sizeof(char), INPUT_FILE_SIZE, INPUT_FILE);
    fclose(INPUT_FILE);
    FILE_CONTENTS[INPUT_FILE_SIZE] = '\0';

    printf("ORIGINAL FILE_CONTENTS=\r\n%s\r\n\r\n",FILE_CONTENTS);

    char *ENCRYPTED = NULL;
    char *DECRYPTED = NULL;

    ENCRYPTED = malloc(PUBLIC_KEY_SIZE);
    RSA_public_encrypt(strlen(FILE_CONTENTS), (unsigned char*)FILE_CONTENTS, (unsigned char*)ENCRYPTED, PUBLIC_KEY, RSA_PKCS1_OAEP_PADDING);

    printf("ENCRYPTED=\r\n%s\r\n\r\n",ENCRYPTED);   

    FILE *FILE_OUT = fopen("BUFFER_ENCRYPTED.TXT", "w");
    fwrite(ENCRYPTED,sizeof(char),strlen(ENCRYPTED),FILE_OUT);
    fclose(FILE_OUT);
    free(ENCRYPTED);
    ENCRYPTED = NULL;

    FILE *FILE_IN = fopen("BUFFER_ENCRYPTED.TXT", "r");     
    fseek(FILE_IN, 0, SEEK_END);
    INPUT_FILE_SIZE = ftell(FILE_IN);
    rewind(FILE_IN);
    FILE_CONTENTS = malloc(PRIVATE_KEY_SIZE);
    fread(FILE_CONTENTS, sizeof(char), PRIVATE_KEY_SIZE, FILE_IN);
    fclose(FILE_IN);

    printf("ENCRYPTED FILE_CONTENTS=\r\n%s\r\n\r\n",FILE_CONTENTS);

    DECRYPTED = malloc(PRIVATE_KEY_SIZE);
    RSA_private_decrypt(PRIVATE_KEY_SIZE, (unsigned char*)FILE_CONTENTS, (unsigned char*)DECRYPTED, PRIVATE_KEY, RSA_PKCS1_OAEP_PADDING);

    printf("DECRYPTED=\r\n%s\r\n\r\n",DECRYPTED);   

    FILE_OUT = fopen("BUFFER_DECRYPTED.TXT", "w");
    fwrite(DECRYPTED,1,strlen(DECRYPTED),FILE_OUT);
    fclose(FILE_OUT);
    free(DECRYPTED);
    DECRYPTED = NULL;

    free(ENCRYPTED);
    ENCRYPTED = NULL;
    free(DECRYPTED);
    DECRYPTED = NULL;
    printf("--- EXAMPLE 2: END---\r\n\r\n");
}

int main(void) {
    int KEY_LENGTH = 2048;
    char *PRIVATE_KEY_FILENAME = "KPRIVATE.PEM";
    char *PUBLIC_KEY_FILENAME = "KPUBLIC.PEM";

    generate_key_pair(KEY_LENGTH,PRIVATE_KEY_FILENAME,PUBLIC_KEY_FILENAME);

    example_one(KEY_LENGTH,PRIVATE_KEY_FILENAME,PUBLIC_KEY_FILENAME);

    example_two(KEY_LENGTH,PRIVATE_KEY_FILENAME,PUBLIC_KEY_FILENAME);

    return 0;
}

RESULT:

--- EXAMPLE 1: BEGIN---

ORIGINAL FILE_CONTENTS=
It is a test!

ENCRYPTED=
◄4ƒþ×^ÖÜ_)'┘ó(¿o╚¡Õßçxô╝♂:9·╗♂l│¿,<õÐ¡+¨═è╣╚IÙL¶,*A1´çØ↔ß%ém¦e  sø¥Qþ¯█‼◄Ð]röwK╠
áWÁ]Úl╗Fv├Æ((Ó*║&^

DECRYPTED=
It is a test!

--- EXAMPLE 1: END---

--- EXAMPLE 2: BEGIN---

ORIGINAL FILE_CONTENTS=
It is a test!

ENCRYPTED=
îþ┘éÑ▬ı;Í5±òM¬ƒ¢ÈkÖ╣┌┬ÆbE☺ã`)[ıó▄■fÞ*ªÄ╚↕ 3É^¾µS86qÜz▬a↑zh▓j´¶È)ë├╬ƒC♂Ë·âÃxÛ╝°ÿ@
Å◄ÈJ~\÷a¼?m▒Ít@♀█ñ¼Ä:£z┤ÀýøGöÞ╩30☼→┘G┬$Ã╩ô°Z‗¢re8►♥k'♫W
ês=ðã;Gfd¬♀@¾þw╚¢Ó_lºóó.├╣ß8┤¼yÝ╚þ┬☼¦è+zP"│┴Isd19Ä£Ç¹×^╣ñ0‼▀Zƒ¾↑}▬.Æãáý·│yCb?ù©u
_|ıƒÀ

ENCRYPTED FILE_CONTENTS=
îþ┘éÑ▬ı;Í5±òM¬ƒ¢ÈkÖ╣┌┬ÆbE☺ã`)[ıó▄■fÞ*ªÄ╚↕ 3É^¾µS86qÜz▬a↑zh▓j´¶È)ë├╬ƒC♂Ë·âÃxÛ╝°ÿ@
Å◄ÈJ~\÷a¼?m▒Ít@♀█ñ¼Ä:£z┤ÀýøGöÞ╩30☼→┘G┬$Ã╩ô°Z‗¢re8►♥k'♫W
ês=ðã;Gfd¬♀@¾þw╚¢Ó_lºóó.├╣ß8┤¼yÝ╚þ┬☼¦è+zP"│┴Isd19Ä£Ç¹×^╣ñ0‼▀Zƒ¾↑}▬.Æãáý·│yCb?ù©u
_|ıƒÀ

DECRYPTED=
It is a test!òM¬ƒ¢ÈkÖ╣┌┬ÆbE☺ã`)[ıó▄■fÞ*ªÄ╚↕ 3É^¾µS86qÜz▬a↑zh▓j´¶È)ë├╬ƒC♂Ë·âÃxÛ╝°
Å◄ÈJ~\÷a¼?m▒Ít@♀█ñ¼Ä:£z┤ÀýøGöÞ╩30☼→┘G┬$Ã╩ô°Z‗¢re8►♥k'♫W
ês=ðã;Gfd¬♀@¾þw╚¢Ó_lºóó.├╣ß8┤¼yÝ╚þ┬☼¦è+zP"│┴Isd19Ä£Ç¹×^╣ñ0‼▀Zƒ¾↑}▬.Æãáý·│yCb?ù©u
_¶ƒÀ,

--- EXAMPLE 2: END---

score 0 · Answer 1 · answered Sep 19 '14 at 01:32

The correct anwser that solve I found on irc #c channel of freenode:

[kadoban] renatokrause: You're treating DECRYPTED as a zero-terminated string. It's not. You need to use the return value of RSA_private_decrypted, which tells you how much data it output

The final code:

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

int generate_key_pair(int KEY_LENGTH, char *PRIVATE_KEY_FILENAME, char *PUBLIC_KEY_FILENAME)
{    
    FILE *KEY_FILE;
    RSA *KEY_PAIR;  
    int RESULT = 0;

    KEY_PAIR = RSA_generate_key(KEY_LENGTH, 17, NULL, NULL);    
    KEY_FILE = fopen(PRIVATE_KEY_FILENAME,"w");
    RESULT = PEM_write_RSAPrivateKey(KEY_FILE, KEY_PAIR, NULL, NULL, 0, NULL, NULL);
    fclose(KEY_FILE);
    KEY_FILE = fopen(PUBLIC_KEY_FILENAME,"w");
    RESULT = (RESULT && PEM_write_RSAPublicKey(KEY_FILE, KEY_PAIR));
    fclose(KEY_FILE);
    return RESULT;
}

void example_one(int KEY_LENGTH, char *PRIVATE_KEY_FILENAME, char *PUBLIC_KEY_FILENAME)
{   
    printf("--- EXAMPLE 1: BEGIN---\r\n\r\n");
    RSA *PUBLIC_KEY = NULL; 
    RSA *PRIVATE_KEY = NULL;
    FILE *KEY_FILE;

    KEY_FILE = fopen(PUBLIC_KEY_FILENAME, "r"); 
    PUBLIC_KEY = PEM_read_RSAPublicKey(KEY_FILE,NULL,NULL,NULL);

    KEY_FILE = fopen(PRIVATE_KEY_FILENAME, "r");    
    PRIVATE_KEY = PEM_read_RSAPrivateKey(KEY_FILE,NULL,NULL,NULL);

    int PUBLIC_KEY_SIZE = RSA_size(PUBLIC_KEY);
    int PRIVATE_KEY_SIZE = RSA_size(PRIVATE_KEY);

    FILE *INPUT_FILE = fopen("BUFFER.TXT", "r");        
    fseek(INPUT_FILE, 0, SEEK_END);
    int INPUT_FILE_SIZE = ftell(INPUT_FILE);
    rewind(INPUT_FILE);
    char *FILE_CONTENTS = malloc(KEY_LENGTH/8);
    fread(FILE_CONTENTS, sizeof(char), INPUT_FILE_SIZE, INPUT_FILE);
    fclose(INPUT_FILE);
    FILE_CONTENTS[INPUT_FILE_SIZE] = '\0';

    printf("ORIGINAL FILE_CONTENTS=\r\n%s\r\n\r\n",FILE_CONTENTS);

    char *ENCRYPTED = NULL;
    char *DECRYPTED = NULL;

    ENCRYPTED = malloc(PUBLIC_KEY_SIZE);
    RSA_public_encrypt(strlen(FILE_CONTENTS), (unsigned char*)FILE_CONTENTS, (unsigned char*)ENCRYPTED, PUBLIC_KEY, RSA_PKCS1_OAEP_PADDING);

    printf("ENCRYPTED=\r\n%s\r\n\r\n",ENCRYPTED);   

    DECRYPTED = malloc(PRIVATE_KEY_SIZE);
    RSA_private_decrypt(PRIVATE_KEY_SIZE, (unsigned char*)ENCRYPTED, (unsigned char*)DECRYPTED, PRIVATE_KEY, RSA_PKCS1_OAEP_PADDING);

    printf("DECRYPTED=\r\n%s\r\n\r\n",DECRYPTED);

    free(ENCRYPTED);
    ENCRYPTED = NULL;
    free(DECRYPTED);
    DECRYPTED = NULL;
    printf("--- EXAMPLE 1: END---\r\n\r\n");
}

void example_two(int KEY_LENGTH, char *PRIVATE_KEY_FILENAME, char *PUBLIC_KEY_FILENAME)
{
    printf("--- EXAMPLE 2: BEGIN---\r\n\r\n");
    RSA *PUBLIC_KEY = NULL; 
    RSA *PRIVATE_KEY = NULL;    
    FILE *KEY_FILE;

    KEY_FILE = fopen(PUBLIC_KEY_FILENAME, "r"); 
    PUBLIC_KEY = PEM_read_RSAPublicKey(KEY_FILE,NULL,NULL,NULL);

    KEY_FILE = fopen(PRIVATE_KEY_FILENAME, "r");    
    PRIVATE_KEY = PEM_read_RSAPrivateKey(KEY_FILE,NULL,NULL,NULL);

    int PUBLIC_KEY_SIZE = RSA_size(PUBLIC_KEY);
    int PRIVATE_KEY_SIZE = RSA_size(PRIVATE_KEY);

    FILE *INPUT_FILE = fopen("BUFFER.TXT", "r");        
    fseek(INPUT_FILE, 0, SEEK_END);
    int INPUT_FILE_SIZE = ftell(INPUT_FILE);
    rewind(INPUT_FILE);
    char *FILE_CONTENTS = malloc(KEY_LENGTH/8);
    fread(FILE_CONTENTS, sizeof(char), INPUT_FILE_SIZE, INPUT_FILE);
    fclose(INPUT_FILE);
    FILE_CONTENTS[INPUT_FILE_SIZE] = '\0';

    printf("ORIGINAL FILE_CONTENTS=\r\n%s\r\n\r\n",FILE_CONTENTS);

    char *ENCRYPTED = NULL;
    char *DECRYPTED = NULL;

    ENCRYPTED = malloc(PUBLIC_KEY_SIZE);
    RSA_public_encrypt(strlen(FILE_CONTENTS), (unsigned char*)FILE_CONTENTS, (unsigned char*)ENCRYPTED, PUBLIC_KEY, RSA_PKCS1_OAEP_PADDING);

    printf("ENCRYPTED=\r\n%s\r\n\r\n",ENCRYPTED);   

    FILE *FILE_OUT = fopen("BUFFER_ENCRYPTED.TXT", "w");
    fwrite(ENCRYPTED,sizeof(char),strlen(ENCRYPTED),FILE_OUT);
    fclose(FILE_OUT);
    free(ENCRYPTED);
    ENCRYPTED = NULL;

    FILE *FILE_IN = fopen("BUFFER_ENCRYPTED.TXT", "r");     
    fseek(FILE_IN, 0, SEEK_END);
    INPUT_FILE_SIZE = ftell(FILE_IN);
    rewind(FILE_IN);
    FILE_CONTENTS = malloc(PRIVATE_KEY_SIZE);
    fread(FILE_CONTENTS, sizeof(char), PRIVATE_KEY_SIZE, FILE_IN);
    fclose(FILE_IN);
    FILE_CONTENTS[INPUT_FILE_SIZE] = '\0';
    printf("ENCRYPTED FILE_CONTENTS=\r\n%s\r\n\r\n",FILE_CONTENTS);

    DECRYPTED = malloc(PRIVATE_KEY_SIZE);
    int DECRYPTED_SIZE = RSA_private_decrypt(PRIVATE_KEY_SIZE, (unsigned char*)FILE_CONTENTS, (unsigned char*)DECRYPTED, PRIVATE_KEY, RSA_PKCS1_OAEP_PADDING);

    printf("DECRYPTED=\r\n%s\r\n\r\n",DECRYPTED);   

    FILE_OUT = fopen("BUFFER_DECRYPTED.TXT", "w");
    fwrite(DECRYPTED,1,DECRYPTED_SIZE,FILE_OUT);
    fclose(FILE_OUT);
    free(DECRYPTED);
    DECRYPTED = NULL;

    free(ENCRYPTED);
    ENCRYPTED = NULL;
    free(DECRYPTED);
    DECRYPTED = NULL;
    printf("--- EXAMPLE 2: END---\r\n\r\n");
}

int main(void) {
    int KEY_LENGTH = 2048;
    char *PRIVATE_KEY_FILENAME = "KPRIVATE.PEM";
    char *PUBLIC_KEY_FILENAME = "KPUBLIC.PEM";

    generate_key_pair(KEY_LENGTH,PRIVATE_KEY_FILENAME,PUBLIC_KEY_FILENAME);

    example_one(KEY_LENGTH,PRIVATE_KEY_FILENAME,PUBLIC_KEY_FILENAME);

    example_two(KEY_LENGTH,PRIVATE_KEY_FILENAME,PUBLIC_KEY_FILENAME);

    return 0;
}

Dropped my answer because telling you the string wasn't terminated apparently wasn't enough (I tried). You may find it very interesting to encrypt a file 245+ chars long using this method. The results may surprise you. — WhozCraig, Sep 19 '14 at 01:43
Its actually less than the modulus size if you're using pkcs1_oaep or regular pkcs1 padding. [**see this question**](http://stackoverflow.com/questions/11822607/what-rsa-max-block-size-to-encode) for more info. Worth your time to brief, including alternatives (two-phase encryption using an AES symmetric key for the data, then RSA for the AES key is talked about). Best of luck. — WhozCraig, Sep 19 '14 at 14:31

Remove dirt in result of decrypt with openssl (C Language)

1 Answers1