Use libtommath to implement the RSA Algorithm

RSAAlgorithmDescription:

1) select two large prime numbers p and q and calculate n = p * q;

2) generate E, D to make:

E * D = 1mod (p-1) (q-1)

E and P-1 (q-1)

[Public Key] e, n

[Private Key] d, n

3) encryption:

C = m ^ d mod n

4) Decryption:

M = C ^ e mod n

Bytes --------------------------------------------------------------------------------------

Libtommath is a large number algorithm library. The followingCodeIt is implemented using the functions in this library, which is quite simple.

# Include <tommath. h> typedef struct {int bits;/* bits in key */mp_int N;/* modulus */mp_int E;/* Public exponent */mp_int D; /* private exponent */} rsa_key; int rsa_rng (unsigned char * DST, int Len, void * dat) {int X; For (x = 0; x <Len; X ++) DST [x] = rand () & 0xff; return Len;} int rsa_preme_random (mp_int * a, int bits) {int err = mp_prime_random_ex (A, 8, BITs, ltm_prime_2msb_on | ltm_prime_safe, rsa_rng, Null); If (Err! = Mp_okay) {return-1;} return 0;} int rsa_gen_key (rsa_key * Key, int bits) {mp_int p, q; mp_int sp, SQ; mp_int n, m; mp_int E, D; mp_int t; // init mp_intsmp_init (& P); mp_init (& Q); mp_init (& SP); mp_init (& sq ); mp_init (& N); mp_init (& M); mp_init (& E); mp_init (& D); mp_init (& T); // genarate P & qrsa_preme_random (& P, bits/2); rsa_preme_random (& Q, bits/2); // make N & MMP _sub_d (& P, 1, & SP); mp_sub_d (& Q, 1, & sq); mp_mul (& P, & Q, & N); mp_mul (& sp, & SQ, & M); // make E & D mp_set (& E, 127); retry_e: mp_gcd (& E, & M, & T); If (mp_cmp_d (& T, 1)> 0) {mp_add_d (& E, 2, & E); goto retry_e;} mp_invmod (& E, & M, & D); // copy n d e to key structmp_init (& Key-> N ); mp_init (& Key-> D); mp_init (& Key-> E); key-> bits = bits; mp_copy (& N, & Key-> N ); mp_copy (& D, & Key-> D); mp_copy (& E, & Key-> E); mp_clear (& P); mp_clear (& Q ); mp_clear (& SP); mp_clear (& sq); mp_clear (& N); mp_clear (& M); mp_clear (& E); mp_clear (& D ); mp_clear (& T); Return 0;}/* Set RSA key by string */INT rsa_set_key (rsa_key * Key, char * sn, char * se, char * SD, int bits, int Radix) {key-> bits = bits; mp_init (& Key-> N); mp_init (& Key-> D ); mp_init (& Key-> E); If (SN) mp_read_radix (& Key-> N, Sn, Radix); If (SE) mp_read_radix (& Key-> E, Se, radix); If (SD) mp_read_radix (& Key-> D, SD, Radix); Return 0 ;}/ * encrypt by private key */INT rsa_encrypt (mp_int * C, mp_int * m, rsa_key * Key) {mp_exptmod (C, & Key-> D, & Key-> n, m); Return 0 ;} /* decrypt by Public Key */INT rsa_decrypt (mp_int * m, mp_int * C, rsa_key * Key) {mp_exptmod (M, & Key-> E, & Key-> N, c); Return 0;} int rsa_test () {mp_intc, M; rsa_key key; char Sn [] = "inherit"; char se [] = "010001 "; char Sm [] = "inherit"; char SC [1024]; mp_init (& C); mp_init (& M); rsa_set_key (& Key, Sn, Se, null, 128, 16); mp_read_radix (& M, Sm, 16); rsa_decrypt (& M, & C, & Key); mp_toradix (& C, SC, 16 ); printf ("% s \ n", SC); return 0 ;}