This library provides a way to easily handle arbitrary large integers.
This library provides the following operations :
- addition, substraction, multiplication, division and modulo
- bits operators (AND, OR, XOR, left and right shifts)
- boolean operators
- modular exponentiation (using montgomery algorithm)
- modular inverse
Example
In this example, we use a 1024 bits long RSA key to encrypt and decrypt a message. We first encrypt the value 0x41 (65 in decimal) and then decrypt it. At the end, m should be equal to 0x41. The encryption is fast (0, 4 second) while the decryption is really slow. This code will take between 30 seconds and 2 minutes to execute depending on the compiler and optimization flags.
main.cpp
#include "mbed.h" #include "BigInt.h" #include <stdlib.h> #include <stdio.h> uint8_t modbits[] = { 0xd9, 0x4d, 0x88, 0x9e, 0x88, 0x85, 0x3d, 0xd8, 0x97, 0x69, 0xa1, 0x80, 0x15, 0xa0, 0xa2, 0xe6, 0xbf, 0x82, 0xbf, 0x35, 0x6f, 0xe1, 0x4f, 0x25, 0x1f, 0xb4, 0xf5, 0xe2, 0xdf, 0x0d, 0x9f, 0x9a, 0x94, 0xa6, 0x8a, 0x30, 0xc4, 0x28, 0xb3, 0x9e, 0x33, 0x62, 0xfb, 0x37, 0x79, 0xa4, 0x97, 0xec, 0xea, 0xea, 0x37, 0x10, 0x0f, 0x26, 0x4d, 0x7f, 0xb9, 0xfb, 0x1a, 0x97, 0xfb, 0xf6, 0x21, 0x13, 0x3d, 0xe5, 0x5f, 0xdc, 0xb9, 0xb1, 0xad, 0x0d, 0x7a, 0x31, 0xb3, 0x79, 0x21, 0x6d, 0x79, 0x25, 0x2f, 0x5c, 0x52, 0x7b, 0x9b, 0xc6, 0x3d, 0x83, 0xd4, 0xec, 0xf4, 0xd1, 0xd4, 0x5c, 0xbf, 0x84, 0x3e, 0x84, 0x74, 0xba, 0xbc, 0x65, 0x5e, 0x9b, 0xb6, 0x79, 0x9c, 0xba, 0x77, 0xa4, 0x7e, 0xaf, 0xa8, 0x38, 0x29, 0x64, 0x74, 0xaf, 0xc2, 0x4b, 0xeb, 0x9c, 0x82, 0x5b, 0x73, 0xeb, 0xf5, 0x49 }; uint8_t dbits[] = { 0x04, 0x7b, 0x9c, 0xfd, 0xe8, 0x43, 0x17, 0x6b, 0x88, 0x74, 0x1d, 0x68, 0xcf, 0x09, 0x69, 0x52, 0xe9, 0x50, 0x81, 0x31, 0x51, 0x05, 0x8c, 0xe4, 0x6f, 0x2b, 0x04, 0x87, 0x91, 0xa2, 0x6e, 0x50, 0x7a, 0x10, 0x95, 0x79, 0x3c, 0x12, 0xba, 0xe1, 0xe0, 0x9d, 0x82, 0x21, 0x3a, 0xd9, 0x32, 0x69, 0x28, 0xcf, 0x7c, 0x23, 0x50, 0xac, 0xb1, 0x9c, 0x98, 0xf1, 0x9d, 0x32, 0xd5, 0x77, 0xd6, 0x66, 0xcd, 0x7b, 0xb8, 0xb2, 0xb5, 0xba, 0x62, 0x9d, 0x25, 0xcc, 0xf7, 0x2a, 0x5c, 0xeb, 0x8a, 0x8d, 0xa0, 0x38, 0x90, 0x6c, 0x84, 0xdc, 0xdb, 0x1f, 0xe6, 0x77, 0xdf, 0xfb, 0x2c, 0x02, 0x9f, 0xd8, 0x92, 0x63, 0x18, 0xee, 0xde, 0x1b, 0x58, 0x27, 0x2a, 0xf2, 0x2b, 0xda, 0x5c, 0x52, 0x32, 0xbe, 0x06, 0x68, 0x39, 0x39, 0x8e, 0x42, 0xf5, 0x35, 0x2d, 0xf5, 0x88, 0x48, 0xad, 0xad, 0x11, 0xa1 }; int main() { BigInt e = 65537, mod, d; mod.importData(modbits, sizeof(modbits)); d.importData(dbits, sizeof(dbits)); BigInt c = modPow(0x41,e,mod); c.print(); BigInt m = modPow(c,d,mod); m.print(); printf("done\n"); return 0; }
Diff: BigInt.cpp
- Revision:
- 12:a436f15b58b6
- Parent:
- 11:2f16a220ebbb
- Child:
- 13:d0b4d7cfeb98
--- a/BigInt.cpp Thu Mar 06 09:44:32 2014 +0000 +++ b/BigInt.cpp Thu Mar 06 10:58:30 2014 +0000 @@ -214,31 +214,33 @@ { assert(a.isValid() && b.isValid()); - BigInt result; - // if a == 0 or b == 0 then result = 0 if(!a || !b) - return result = 0; + return 0; // if a == 1, then result = b if(a == 1) - return (result = b); + return b; // if b == 1, then result = a if(b == 1) - return (result = a); - + return a; + + BigInt result; result.size = a.size + b.size; result.bits = new uint32_t[num(result.size)]; - memset(result.bits, 0, result.size); + memset(result.bits, 0, sizeof(uint32_t)*num(result.size)); for(int i = 0; i < num(a.size); ++i) { uint64_t carry = 0; for(int j = 0; j < num(b.size); ++j) { uint64_t tmp = (uint64_t)a.bits[i] * (uint64_t)b.bits[j] + carry; + uint32_t t = result.bits[i+j]; result.bits[i+j] += tmp; - carry = tmp >> 32; + carry = tmp >> 32; + if(t > result.bits[i+j]) + ++carry; } if(carry != 0) result.bits[i+num(b.size)] += carry; @@ -265,12 +267,10 @@ if(a == b) return 1; BigInt u = a; - printf("a.bits = %d\n", a.numBits()); int m = a.numBits() - b.numBits(); - printf("m=%d\n", m); BigInt q = 0; - BigInt tmp = b << m; - + BigInt tmp = b; + tmp <<= m; for(int j = m; j >= 0; --j) { if(tmp <= u) @@ -278,7 +278,7 @@ u -= tmp; BigInt tmp2 = 1; tmp2 <<= j; - q += tmp2; + q += tmp2; } tmp >>= 1; } @@ -295,13 +295,12 @@ { assert(a.isValid()); + if(m == 0) + return a; + if(m/8 >= a.size) + return 0; + BigInt result; - - if(m == 0) - return result = a; - if(m/8 >= a.size) - return result = 0; - result.size = a.size - m/8; result.bits = new uint32_t[num(result.size)]; uint8_t s = m%32; @@ -334,7 +333,7 @@ result.size = m/8 + a.size; uint32_t h = a.bits[num(a.size)-1]; - if((h << (m%32)) < h) + if((m%32)%8 != 0) ++result.size; uint32_t l = num(result.size); result.bits = new uint32_t[l]; @@ -347,9 +346,10 @@ else result.bits[m/32+i] = (a.bits[i] << s) | (a.bits[i-1] >> (32-s)); } - if(a.bits[num(a.size)-1] << s < a.bits[num(a.size)-1]) - result.bits[num(result.size)-1] = a.bits[num(a.size)-1] >> (32-s); + if(a.bits[num(a.size)-1] && s != 0) + result.bits[m/32+num(result.size)-1] |= a.bits[num(a.size)-1] >> (32-s); + result.trim(); return result; } @@ -362,19 +362,7 @@ BigInt operator%(const BigInt &a, const BigInt &b) { assert(a.isValid() && b.isValid() && b > 0); - - BigInt i = 1, result; - - while(a >= b*i && a < b*(i+1)) - { - ++i; - } - --i; - result = a - b*i; - - result.trim(); - - return result; + return a - (a/b)*b; } BigInt& BigInt::operator%=(const BigInt &a) @@ -411,8 +399,12 @@ return false; uint32_t l = num(a.size); for(int i = l-1; i >= 0; --i) + { if(a.bits[i] < b.bits[i]) return true; + else if(a.bits[i] > b.bits[i]) + return false; + } return false; } @@ -431,8 +423,12 @@ return false; uint32_t l = num(a.size); for(int i = l-1; i >= 0; --i) + { if(a.bits[i] > b.bits[i]) return true; + else if(a.bits[i] < b.bits[i]) + return false; + } return false; } @@ -571,7 +567,7 @@ BigInt tmp2 = 1; tmp2 = 1 << r; tmp2 *= a; - BigInt montA = tmp2 - tmp2/modulus; + BigInt montA = tmp2%modulus; montA.print(); BigInt tmp = montA; BigInt tmpE = expn; @@ -621,9 +617,7 @@ uint32_t BigInt::numBits() const { assert(isValid()); - - print(); - + uint32_t n = (size-1)*8; uint8_t a = bits[num(size)-1] >> ((size-1)%4)*8; uint8_t tmp2 = 8;