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| #include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <gmp.h>
#define ENCRYPTION_EXPONENT 65537 /* X.509, PKCS#1 */
#define ENCRYPTION_EXPONENT2 17
#define ENCRYPTION_EXPONENT3 3 /* PEM, PKCS#1 */
#define EXTENSION_LENGTH 9
#define LOG_2 ((double) 0.301029995667)
#define MAX_FILENAME 500
#define MAX_PRIME_DIGITS 666
#define MAX_PRIME_RANGE 5000
#define MAX_PROB_REPS 30
#define RANDMASK 63 + 1
#define WORD_BIT_SIZE 32
void doProbPrimes(void);
void enCrypt();
void deCrypt();
void keyGen(void);
char *menuText =
" (1) Generate probabilistic primes\n"
" (2) Encrypt a message\n"
" (3) Decrypt a message\n"
" (4) Generate public/private keypair\n"
" (0) Quit\n"
"\n"
"Choice: ";
int
main (int argc, char **argv) {
int choice;
/* seed the PRNG */
srandom(time(NULL));
printf("%s\n",banner);
/* process input selections from menu */
while (1) {
printf("%s",menuText);
fflush(stdout);
scanf("%d",&choice);
fflush(stdin);
switch(choice) {
case 0: /* end program */
exit(0);
break;
case 1: /* probabilistic primes */
doProbPrimes();
break;
case 2: /* encrypt a file */
enCrypt();
break;
case 3: /* decrypt a file */
deCrypt();
break;
case 4: /* generate pub/priv keypair */
keyGen();
break;
}
}
}
void
doProbPrimes(void) {
char num[MAX_PRIME_DIGITS+1];
mpz_t userIn,x;
int i;
printf("Enter a starting number up to %d digits in length.\n",MAX_PRIME_DIGITS);
printf("Probabilistic primes p in the range:\n");
printf(" x <= p <= x + %d\n",MAX_PRIME_RANGE);
printf("will be found.\n");
printf("Number: ");
fflush(stdout);
fgets(num,MAX_PRIME_DIGITS+1,stdin);
/* initialize the integer type */
mpz_init_set_str(userIn,num,10);
mpz_init(x);
/* if it's even, add 1... */
if(!mpz_mod_ui(x,userIn,2)) {
mpz_add_ui(x,userIn,1);
}
else {
mpz_set(x,userIn);
}
/* loop through...skipping evens since they're not prime */
for(i=0;i<MAX_PRIME_RANGE/2;i++) {
mpz_add_ui(x,x,2);
/* if gmp thinks it's a probabilistic prime, it works for us... */
if(mpz_probab_prime_p(x,MAX_PROB_REPS)) {
printf("%s\n",mpz_get_str(NULL,10,x));
}
}
mpz_clear(userIn);
mpz_clear(x);
}
/**
* enCrypt()
*
* Encrypt a specified text file with an RSA public key
*/
void
enCrypt(void) {
char keyFile[MAX_FILENAME+EXTENSION_LENGTH+1], encryptFile[MAX_FILENAME+1];
char outFile[MAX_FILENAME+1];
FILE *PK,*OF;
mpz_t e,n,m,c;
int blockSize, *block, i, j;
char *cBlock, scratch[4];
/* initialize our integers */
mpz_init(e);
mpz_init(n);
mpz_init(m);
mpz_init(c);
/* grab name of file to encrypt */
printf("Enter filename to encrypt\n");
fgets(encryptFile,MAX_FILENAME+1,stdin);
encryptFile[strlen(encryptFile)-1] = NULL;
/* grab name of ciphertext */
printf("Enter filename to store ciphertext in\n");
fgets(outFile,MAX_FILENAME+1,stdin);
outFile[strlen(outFile)-1] = NULL;
/* grab name of keyfile */
printf("Enter filename for the public key to encrypt this file with\n");
printf("WITHOUT the .public extension\n");
fgets(keyFile,MAX_FILENAME+1,stdin);
keyFile[strlen(keyFile)-1] = NULL;
strcat(keyFile,".public");
/* read in key */
PK=fopen(keyFile,"r");
mpz_inp_str(e,PK,10);
mpz_inp_str(n,PK,10);
fclose(PK);
#if 0
printf("e = %s\n",mpz_get_str(NULL,10,e));
printf("n = %s\n",mpz_get_str(NULL,10,n));
#endif
/* compute blocksize */
blockSize = (strlen(mpz_get_str(NULL,10,n)) - 1) / 3;
block = calloc(blockSize+1, sizeof(int));
cBlock = calloc(3 * blockSize + 1, sizeof(char));
#if 0
printf("blockSize = %d\n",blockSize);
#endif
PK=fopen(encryptFile,"r");
OF=fopen(outFile,"w+");
/* loop thru plaintext, reading in blocks */
while(!feof(PK)) {
/* read in enough chars for block */
for(i=0;i<blockSize && !feof(PK);i++) {
block[i] = fgetc(PK);
if(block[i] == EOF) {
block[i] = 0;
break;
}
else if((block[i] < 32) || (block[i] > 127))
block[i] = ' ';
block[i+1]=0;
}
/* concat decimal representations */
for(j=0;j<i;j++) {
sprintf(scratch,"%d",block[j]);
strcat(cBlock,scratch);
}
/* put string into integer type */
mpz_set_str(m,cBlock,10);
/* c = (m^e) % n ... RSA encryption */
mpz_powm(c,m,e,n);
/* write out encrypted block */
mpz_out_str(OF,10,c);
fprintf(OF,"\n");
cBlock[0]='\0';
}
fclose(PK);
fclose(OF);
mpz_clear(e);
mpz_clear(n);
mpz_clear(m);
mpz_clear(c);
free(cBlock);
free(block);
}
/**
* deCrypt()
*
* Decrypt a specified text file with an RSA private key
*/
void
deCrypt(void) {
char keyFile[MAX_FILENAME+EXTENSION_LENGTH+1], decryptFile[MAX_FILENAME+1];
char outFile[MAX_FILENAME+1];
FILE *PK,*OF;
mpz_t d,n,m,c;
int blockSize, i, j;
char *cBlock, scratch[4];
/* init ints */
mpz_init(d);
mpz_init(n);
mpz_init(m);
mpz_init(c);
/* grab name of file to decrypt */
printf("Enter filename to decrypt\n");
fgets(decryptFile,MAX_FILENAME+1,stdin);
decryptFile[strlen(decryptFile)-1] = NULL;
/* grab name of plaintext file */
printf("Enter filename to store plaintext in\n");
fgets(outFile,MAX_FILENAME+1,stdin);
outFile[strlen(outFile)-1] = NULL;
/* grab name of keyfile */
printf("Enter filename for the private key to decrypt this file with\n");
printf("WITHOUT the .private extension\n");
fgets(keyFile,MAX_FILENAME+1,stdin);
keyFile[strlen(keyFile)-1] = NULL;
strcat(keyFile,".private");
/* read in private key */
PK=fopen(keyFile,"r");
mpz_inp_str(d,PK,10);
mpz_inp_str(n,PK,10);
fclose(PK);
#if 0
printf("d = %s\n",mpz_get_str(NULL,10,d));
printf("n = %s\n",mpz_get_str(NULL,10,n));
#endif
/* calculate size of character block */
cBlock = calloc(mpz_sizeinbase(n,10)+2,sizeof(char));
PK=fopen(decryptFile,"r");
OF=fopen(outFile,"w+");
/* loop through encrypted blocks, decrypting them */
while(!feof(PK) && mpz_inp_str(c,PK,10)) {
/* m = (c^d) % n ... RSA decryption */
mpz_powm(m,c,d,n);
mpz_get_str(cBlock,10,m);
#if 0
printf("cBlock = %s\n",cBlock);
#endif
/* loop through decrypted block, separating out individual
* characters
*/
for(i=0;i<strlen(cBlock);i++) {
if(cBlock[i] == '1') {
scratch[0] = cBlock[i]; i++;
scratch[1] = cBlock[i]; i++;
scratch[2] = cBlock[i];
scratch[3] = '\0';
}
else {
scratch[0] = cBlock[i]; i++;
scratch[1] = cBlock[i];
scratch[2] = '\0';
scratch[3] = '\0';
}
fprintf(OF,"%c",atoi(scratch));
}
fprintf(OF,"\n");
}
fclose(PK);
fclose(OF);
mpz_clear(d);
mpz_clear(n);
mpz_clear(m);
mpz_clear(c);
free(cBlock);
}
/**
* keyGen()
*
* Generate a public/private RSA keypair
*/
void
keyGen(void) {
int userDigits,rLimbs,i,r;
mpz_t randInt1,randInt2,p,q,n,phi_n,e,d,p_1,q_1,foo;
char fname[MAX_FILENAME+1], pubFname[MAX_FILENAME+EXTENSION_LENGTH+1];
char privFname[MAX_FILENAME+EXTENSION_LENGTH+1];
FILE *PUBF, *PRIVF;
/* get an incredibly rough approximation of the number of digits to
* use for the primes.... This is coarse because mp uses the concept
* of "limbs" when generating random numbers....basically machine words,
* so the # of digits only determines how many limbs... The primes are
* always AT LEAST the number of digits the user specifies.
*/
do {
printf("Enter the (ROUGH) approximate number of digits you want\n");
printf("your RSA primes to be (min 12, max %d).\n\n",MAX_PRIME_DIGITS);
printf("Size: ");
fflush(stdout);
scanf("%d",&userDigits);
fflush(stdin);
} while((userDigits < 12) || (userDigits > MAX_PRIME_DIGITS));
/* figure out how many limbs will hold the specified number of digits */
rLimbs = ((((double) userDigits) / LOG_2) / ((double) WORD_BIT_SIZE)) + 1;
#if 0
printf("limbs: %d %f\n",rLimbs,((double) userDigits) / LOG_2);
#endif
mpz_init(randInt1);
mpz_init(randInt2);
mpz_init(p);
mpz_init(q);
mpz_init(p_1);
mpz_init(q_1);
mpz_init(n);
mpz_init(phi_n);
mpz_init(e);
mpz_init(d);
mpz_init(foo);
/* find a random starting point for p...since there's no mpz_srandom,
* find a random number of random numbers first
*/
do {
r=random() & RANDMASK;
for(i=0;i<r;i++)
mpz_random(randInt1,rLimbs);
} while(strlen(mpz_get_str(NULL,10,randInt1)) < userDigits);
mpz_set(p,randInt1);
/* keep looking for probabilistic primes */
while(!mpz_probab_prime_p(p,MAX_PROB_REPS)) {
mpz_add_ui(p,p,1);
}
printf("p = %s\n",mpz_get_str(NULL,10,p));
/* find a random starting point for q...since there's no mpz_srandom,
* find a random number of random numbers first
*/
do {
r=random() & RANDMASK;
for(i=0;i<r;i++)
mpz_random(randInt2,rLimbs);
} while(strlen(mpz_get_str(NULL,10,randInt2)) < userDigits);
mpz_set(q,randInt2);
/* keep looking for probabilistic primes */
while(!mpz_probab_prime_p(q,MAX_PROB_REPS)) {
mpz_add_ui(q,q,1);
}
printf("q = %s\n",mpz_get_str(NULL,10,q));
/* find n */
mpz_mul(n,p,q);
printf("n = %s\n",mpz_get_str(NULL,10,n));
/* find phi(n) */
mpz_sub_ui(p_1,p,1);
mpz_sub_ui(q_1,q,1);
mpz_mul(phi_n,p_1,q_1);
printf("phi(n) = %s\n",mpz_get_str(NULL,10,phi_n));
*/
mpz_set_ui(e,ENCRYPTION_EXPONENT);
printf("e = %s\n",mpz_get_str(NULL,10,e));
/* find d */
mpz_invert(d,e,phi_n);
printf("d = %s\n",mpz_get_str(NULL,10,d));
/* just for the hell of it, show that it works... */
mpz_mul(foo,e,d);
mpz_mod(foo,foo,phi_n);
printf("e * d %% n = %s\n",mpz_get_str(NULL,10,foo));
/* get filename for the pub/priv keys */
printf("Enter filename to write out to (e.g. \"foo\" would give foo.public, foo.private)\n");
printf("or just hit return to not save.\n");
fgets(fname,MAX_FILENAME+1,stdin);
fname[strlen(fname)-1] = NULL;
if(fname[0] != NULL) {
strcpy(pubFname,fname);
strcat(pubFname,".public");
strcpy(privFname,fname);
strcat(privFname,".private");
/* write out public key */
PUBF=fopen(pubFname,"w+t");
mpz_out_str(PUBF,10,e);
fprintf(PUBF,"\n");
mpz_out_str(PUBF,10,n);
fprintf(PUBF,"\n");
fclose(PUBF);
/* write out private key */
PRIVF=fopen(privFname,"w+t");
mpz_out_str(PRIVF,10,d);
fprintf(PRIVF,"\n");
mpz_out_str(PRIVF,10,n);
fprintf(PRIVF,"\n");
fclose(PRIVF);
}
mpz_clear(randInt1);
mpz_clear(randInt2);
mpz_clear(p);
mpz_clear(q);
mpz_clear(p_1);
mpz_clear(q_1);
mpz_clear(n);
mpz_clear(phi_n);
mpz_clear(e);
mpz_clear(d);
} |
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