54 lines
1.4 KiB
Plaintext
54 lines
1.4 KiB
Plaintext
extern crate num;
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use num::bigint::BigUint;
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use num::integer::Integer;
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use num::traits::{One, Zero};
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fn mod_exp(b: &BigUint, e: &BigUint, n: &BigUint) -> Result<BigUint, &'static str> {
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if n.is_zero() {
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return Err("modulus is zero");
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}
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if b >= n {
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// base is too large and should be split into blocks
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return Err("base is >= modulus");
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}
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if b.gcd(n) != BigUint::one() {
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return Err("base and modulus are not relatively prime");
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}
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let mut bb = b.clone();
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let mut ee = e.clone();
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let mut result = BigUint::one();
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while !ee.is_zero() {
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if ee.is_odd() {
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result = (result * &bb) % n;
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}
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ee >>= 1;
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bb = (&bb * &bb) % n;
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}
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Ok(result)
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}
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fn main() {
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let msg = "Rosetta Code";
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let n = "9516311845790656153499716760847001433441357"
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.parse()
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.unwrap();
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let e = "65537".parse().unwrap();
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let d = "5617843187844953170308463622230283376298685"
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.parse()
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.unwrap();
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let msg_int = BigUint::from_bytes_be(msg.as_bytes());
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let enc = mod_exp(&msg_int, &e, &n).unwrap();
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let dec = mod_exp(&enc, &d, &n).unwrap();
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let msg_dec = String::from_utf8(dec.to_bytes_be()).unwrap();
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println!("msg as txt: {}", msg);
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println!("msg as num: {}", msg_int);
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println!("enc as num: {}", enc);
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println!("dec as num: {}", dec);
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println!("dec as txt: {}", msg_dec);
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}
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