Create RSAcipher(Big).go

An alternate implementation of RSA using the math/rand library. Uses 1024 bit encryption

Author: 0xbrayo

ciphers/RSAcipher(Big).go

@@ -0,0 +1,128 @@
+package main
+
+import (
+	"math/big"
+	crypto"crypto/rand"
+	"strconv"
+	"fmt"
+)
+/*
+Care has been taken to uses cryptographic secure functions
+The primes numbers are 1024 bits which is as secure as u can get really
+crypto/rand library has been imported as crypto and not rand
+This import style will make it easier to spot all the cryptographic secure functions
+*/
+func main(){
+	p,_:= crypto.Prime(crypto.Reader,1024)
+	q,_:= crypto.Prime(crypto.Reader,1024)
+	if !(primeCheck(p)||primeCheck(q)){
+		//they are always prime, no worries
+		fmt.Println("These numbers ain't prime")
+	}
+	n := new(big.Int).Mul(p,q)
+	
+	one := big.NewInt(1)
+
+	delta := lcmBig(p.Sub(p,one),q.Sub(q,one))
+
+	e,_:= crypto.Prime(crypto.Reader,delta.BitLen())
+	d := big.NewInt(0)
+	d.ModInverse(e,delta)
+
+	cleartext := "Black Lives Matter, all lives can't matter until Black lives matter"
+	runes :=[]rune(cleartext)
+	ASCIIs :=toASCII(runes)
+	stringEncoded := stringEncode(ASCIIs)
+	bigNum, _ :=  new(big.Int).SetString(stringEncoded,0)
+	/*
+	TODO: check that bigNum is not larger than N if larger break
+	into two or more strings and encrypt separately
+	*/
+	fmt.Printf("Message to be encrypted: %v \n",cleartext)
+	fmt.Printf("ASCII encoded: %v\n",bigNum)
+	encrypted := encryptBig(bigNum,e,n)
+	fmt.Printf("ciphertext: %v \n",encrypted)
+	decrypted := decryptBig(encrypted,d,n)
+	fmt.Printf("Decrypted but still ASCII encoded: %v \n",decrypted)
+	decryptASCIIs := stringDecode(decrypted)
+	fmt.Printf("Plaintext (original message) :%v",toRune(decryptASCIIs))
+}
+
+func encryptBig(num *big.Int, privateExponent *big.Int, modulus *big.Int)*big.Int{
+	//encrypts by modular exponentiation
+	encrypted := new(big.Int).Exp(num,privateExponent,modulus)
+	return encrypted
+}
+
+func decryptBig(num *big.Int, publicExponent *big.Int, modulus *big.Int)*big.Int{
+	//decrypts by modular exponentiation
+	decrypted := new(big.Int).Exp(num,publicExponent,modulus)
+	return decrypted
+}
+
+func lcmBig(x *big.Int, y *big.Int)*big.Int{
+	//an lcm implementation for big.Int numbers
+	gcd := new(big.Int).GCD(nil,nil,x,y)
+	temp :=  new(big.Int).Mul(x,y)
+	lcm :=  new(big.Int).Div(temp,gcd)
+	return lcm
+}
+
+func primeCheck(prime *big.Int)bool{
+	//primality test
+	return prime.ProbablyPrime(256)
+}
+
+func toASCII(slice []rune)[]int{
+	//runs in O(n) where n = len(slice)
+	var converted []int
+	for _,v:= range slice{
+		converted = append(converted, int(v))
+	}
+	return converted
+}
+
+func toRune(slice []int)string{
+	//runs in O(n) where n = len(slice)
+	var str string
+	for _,v:= range slice{
+		str += string(v)
+	}
+	return str
+}
+
+func stringEncode(slice []int)string{
+	//encodes the ASCII to a string 
+	var out []string
+	for _,v := range slice{
+	if v<100 {
+		out =append(out,"0"+strconv.Itoa(v))
+		continue
+		}
+	out = append(out, strconv.Itoa(v))
+	}
+	var str string
+	for _,v := range out{
+		str += v
+	}
+	/*strips leading 0 if present to avoid conversion errors
+	*/
+	if str[0]== '0'{
+		str = str[1:]
+	}
+	return str
+}
+
+func stringDecode(decryptedBig *big.Int)[]int{
+	//decodes the number to string then ASCII values
+	str := decryptedBig.String()
+	if len(str)%3!=0{
+		str ="0"+str
+	}
+	var ASCII []int 
+	for i:=0; i<len(str); i+=3{
+		temp,_:= strconv.Atoi(str[i:i+3])
+		ASCII = append(ASCII,temp)
+	}
+	return ASCII
+}