RSA … GNU MP: Cannot allocate memory (size=1307836444)

问题

To start, I'm running Ubuntu 12.04 32-bit. This program does RSA pub key crypto by taking cin into a char buffer. Then, when I call my encrypt function, I get the following error:

GNU MP: Cannot allocate memory (size=1307836444)
Aborted (core dumped)

When I change the bit-size of the p,q keys I generate, the size in this run-time error increases. This error happens only after I call encrypt().

void generate_pq(mpz_t p, mpz_t q);
void compute_n(mpz_t n, const mpz_t p, const mpz_t q);
void compute_phiN(mpz_t phi_n, const mpz_t p, const mpz_t q);
void select_e(mpz_t e, mpz_t phi_n);
void compute_d(mpz_t d, mpz_t e, mpz_t phi_n);
void store_m(mpz_t m[], int& size);
void encrypt(mpz_t c[], mpz_t m[], const int size, 
                 const mpz_t e, const mpz_t n);
void decrypt(mpz_t m2[], mpz_t c[], const int size, 
                 const mpz_t d, const mpz_t n);

int main() 
{
    mpz_t p, q, n, phi_n, e, d; 
    mpz_inits(p, q, n, phi_n, e, d, NULL);

    // 1. Generate p,q; compute n
    generate_pq(p,q);
    compute_n(n,p,q);
    // 2. Compute phi(n)=(p-1)*(q-1)
    compute_phiN(phi_n,p,q);
    mpz_clear(p); mpz_clear(q);
    // 3. Select encryption key e
    select_e(e,phi_n);
    // 4. Compute decryption key d
    compute_d(d,e,phi_n);
    // 5. m = message to be encrypted
    mpz_t* m;
    int size=0;
    store_m(m,size);
    // 6. c = encrypted message
    mpz_t* c;
    encrypt(c,m,size,e,n);
    // 7. m2 = decrypted message 
    //mpz_t* m2;
    //decrypt(m2,c,size,d,n);
    return 0;
}

Compiled using...

g++ -o rsa partb.cc -lgmpxx -lgmp

I have tried using mpz_clear in the for-loops for m, c, and m2. No change. Here is the encrypt function:

void store_m(mpz_t m[], int& size) 
{
    printf("Message: ");
    char* buffer = new char[128];
    cin.getline(buffer,128);
    size = strlen(buffer); //size = buffer
    m = new mpz_t[size];
    for(int i=0; i<size; i++) {
        mpz_init(m[i]);
        mpz_set_ui(m[i],(int)buffer[i]);
    }
}

void encrypt(mpz_t c[], mpz_t m[], const int size, 
                 const mpz_t e, const mpz_t n)
{ /* c = cipher */
    c = new mpz_t[size];
    for(int i=0; i<size; i++) {
        mpz_init(c[i]);
        mpz_powm(c[i],m[i],e,n);
        mpz_clear(m[i]);
    } /* c = m^e(mod n) */
}

Perhaps the issue is that I am not deallocating enough of the mpz_t's that I have declared and initialized? I tried clearing 2 or 3 of the mpz_t's but it didn't seem to have an effect. Please advise.

EDIT!!!!!!!!

Isolated the seg fault to this statement:

mpz_powm(c[i],m[i],e,n);

回答1:

Your variable mpz_t* c is not changed by the encrypt function, so it still points to a random (probably invalid) address after encrypt returns. Try instead:

void encrypt(mpz_t*& c,...

来源：https://stackoverflow.com/questions/20127204/rsa-gnu-mp-cannot-allocate-memory-size-1307836444

标签

c++

encryption

rsa

gmp