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fix blinding and fold in new impl
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@dignifiedquire
dignifiedquire committed Nov 29, 2023
1 parent 98a86a2 commit f4131c5
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Showing 4 changed files with 68 additions and 198 deletions.
3 changes: 1 addition & 2 deletions Cargo.lock
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3 changes: 3 additions & 0 deletions Cargo.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -65,3 +65,6 @@ rustdoc-args = ["--cfg", "docsrs"]

[profile.dev]
opt-level = 2

[patch.crates-io]
crypto-bigint = { git = "https://github.com/RustCrypto/crypto-bigint", branch = "master" }
220 changes: 63 additions & 157 deletions src/algorithms/rsa.rs
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Original file line number Diff line number Diff line change
@@ -1,10 +1,9 @@
//! Generic RSA implementation
use alloc::borrow::Cow;
use alloc::vec::Vec;
use crypto_bigint::modular::BoxedResidueParams;
use crypto_bigint::{BoxedUint, NonZero};
use num_bigint::{BigInt, BigUint, IntoBigInt, IntoBigUint, ModInverse, RandBigInt, ToBigInt};
use crypto_bigint::{BoxedUint, RandomMod};
use num_bigint::{BigUint, IntoBigInt, IntoBigUint, ModInverse, ToBigInt};
use num_integer::{sqrt, Integer};
use num_traits::{FromPrimitive, One, Pow, Signed, Zero as _};
use rand_core::CryptoRngCore;
Expand All @@ -14,7 +13,7 @@ use zeroize::{Zeroize, Zeroizing};
use crate::errors::{Error, Result};
use crate::key::{reduce, to_biguint, to_uint};
use crate::traits::keys::{PrivateKeyPartsNew, PublicKeyPartsNew};
use crate::traits::{PrivateKeyParts, PublicKeyParts};
use crate::traits::PublicKeyParts;

/// ⚠️ Raw RSA encryption of m with the public key. No padding is performed.
///
Expand All @@ -38,25 +37,35 @@ pub fn rsa_encrypt<K: PublicKeyParts>(key: &K, m: &BigUint) -> Result<BigUint> {
#[inline]
pub fn rsa_decrypt<R: CryptoRngCore + ?Sized>(
mut rng: Option<&mut R>,
priv_key: &impl PrivateKeyParts,
c: &BigUint,
priv_key: &impl PrivateKeyPartsNew,
c_orig: &BigUint,
) -> Result<BigUint> {
if c >= &priv_key.n() {
// convert to crypto bigint
let c = to_uint(c_orig.clone());
let n = priv_key.n();
let d = priv_key.d();

if c >= **n {
return Err(Error::Decryption);
}

if priv_key.n().is_zero() {
// TODO: is this fine?
if n.is_zero().into() {
return Err(Error::Decryption);
}

let mut ir = None;

let n_params = priv_key
.residue_params()
.cloned()
.unwrap_or_else(|| BoxedResidueParams::new(n.clone().get()).unwrap());
let c = if let Some(ref mut rng) = rng {
let (blinded, unblinder) = blind(rng, priv_key, c);
let (blinded, unblinder) = blind(rng, priv_key, &c, &n_params);
ir = Some(unblinder);
Cow::Owned(blinded)
blinded
} else {
Cow::Borrowed(c)
c
};

let dp = priv_key.dp();
Expand All @@ -68,19 +77,21 @@ pub fn rsa_decrypt<R: CryptoRngCore + ?Sized>(
(Some(dp), Some(dq), Some(qinv), Some(crt_values)) => {
// We have the precalculated values needed for the CRT.

let p = &priv_key.primes()[0];
let q = &priv_key.primes()[1];
let dp = to_biguint(dp);
let dq = to_biguint(dq);
let qinv = to_biguint(qinv).to_bigint().unwrap();
let p = to_biguint(&priv_key.primes()[0]);
let q = to_biguint(&priv_key.primes()[1]);

let mut m = c.modpow(&dp, p).into_bigint().unwrap();
let mut m2 = c.modpow(&dq, q).into_bigint().unwrap();
let mut m = c_orig.modpow(&dp, &p).into_bigint().unwrap();
let mut m2 = c_orig.modpow(&dq, &q).into_bigint().unwrap();

m -= &m2;

let mut primes: Vec<_> = priv_key
.primes()
.iter()
.map(ToBigInt::to_bigint)
.map(Option::unwrap)
.map(|p| to_biguint(p).to_bigint().unwrap())
.collect();

while m.is_negative() {
Expand All @@ -91,17 +102,17 @@ pub fn rsa_decrypt<R: CryptoRngCore + ?Sized>(
m *= &primes[1];
m += &m2;

let mut c = c.into_owned().into_bigint().unwrap();
let mut c = c_orig.to_bigint().unwrap();
for (i, value) in crt_values.iter().enumerate() {
let prime = &primes[2 + i];
m2 = c.modpow(&value.exp, prime);
m2 = c.modpow(&to_biguint(&value.exp).to_bigint().unwrap(), prime);
m2 -= &m;
m2 *= &value.coeff;
m2 *= &to_biguint(&value.coeff).to_bigint().unwrap();
m2 %= prime;
while m2.is_negative() {
m2 += prime;
}
m2 *= &value.r;
m2 *= &to_biguint(&value.r).to_bigint().unwrap();
m += &m2;
}

Expand All @@ -113,17 +124,21 @@ pub fn rsa_decrypt<R: CryptoRngCore + ?Sized>(
c.zeroize();
m2.zeroize();

m.into_biguint().expect("failed to decrypt")
to_uint(m.into_biguint().expect("failed to decrypt"))
}
_ => {
let c = reduce(&c, n_params);
c.pow(&d).retrieve()
}
_ => c.modpow(&priv_key.d(), &priv_key.n()),
};

match ir {
Some(ref ir) => {
// unblind
Ok(unblind(priv_key, &m, ir))
let res = to_biguint(&unblind(priv_key, &m, ir));
Ok(res)
}
None => Ok(m),
None => Ok(to_biguint(&m)),
}
}

Expand All @@ -138,29 +153,11 @@ pub fn rsa_decrypt<R: CryptoRngCore + ?Sized>(
/// or signature scheme. See the [module-level documentation][crate::hazmat] for more information.
#[inline]
pub fn rsa_decrypt_and_check<R: CryptoRngCore + ?Sized>(
priv_key: &impl PrivateKeyParts,
rng: Option<&mut R>,
c: &BigUint,
) -> Result<BigUint> {
let m = rsa_decrypt(rng, priv_key, c)?;

// In order to defend against errors in the CRT computation, m^e is
// calculated, which should match the original ciphertext.
let check = rsa_encrypt(priv_key, &m)?;

if c != &check {
return Err(Error::Internal);
}

Ok(m)
}

pub fn rsa_decrypt_and_check_new<R: CryptoRngCore + ?Sized>(
priv_key: &impl PrivateKeyPartsNew,
rng: Option<&mut R>,
c: &BigUint,
) -> Result<BigUint> {
let m = rsa_decrypt_new(rng, priv_key, c)?;
let m = rsa_decrypt(rng, priv_key, c)?;

// In order to defend against errors in the CRT computation, m^e is
// calculated, which should match the original ciphertext.
Expand All @@ -174,38 +171,40 @@ pub fn rsa_decrypt_and_check_new<R: CryptoRngCore + ?Sized>(
}

/// Returns the blinded c, along with the unblinding factor.
fn blind<R: CryptoRngCore, K: PublicKeyParts>(
fn blind<R: CryptoRngCore, K: PublicKeyPartsNew>(
rng: &mut R,
key: &K,
c: &BigUint,
) -> (BigUint, BigUint) {
c: &BoxedUint,
n_params: &BoxedResidueParams,
) -> (BoxedUint, BoxedUint) {
// Blinding involves multiplying c by r^e.
// Then the decryption operation performs (m^e * r^e)^d mod n
// which equals mr mod n. The factor of r can then be removed
// by multiplying by the multiplicative inverse of r.

let mut r: BigUint;
let mut ir: Option<BigInt>;
let mut r: BoxedUint;
let mut ir: CtOption<BoxedUint>;
let unblinder;
loop {
r = rng.gen_biguint_below(&key.n());
if r.is_zero() {
r = BigUint::one();
// TODO: use constant time gen
r = BoxedUint::random_mod(rng, key.n());
// TODO: correct mapping
if r.is_zero().into() {
r = BoxedUint::one();
}
ir = r.clone().mod_inverse(key.n());
if let Some(ir) = ir {
if let Some(ub) = ir.into_biguint() {
unblinder = ub;
break;
}
ir = r.inv_mod(key.n());

// TODO: constant time?
if let Some(ir) = ir.into() {
unblinder = ir;
break;
}
}

let c = {
let mut rpowe = r.modpow(&key.e(), &key.n()); // N != 0
let mut c = c * &rpowe;
c %= key.n();

let r = reduce(&r, n_params.clone());
let mut rpowe = r.pow(key.e()).retrieve();
let c = c.mul_mod(&rpowe, key.n());
rpowe.zeroize();

c
Expand All @@ -215,8 +214,8 @@ fn blind<R: CryptoRngCore, K: PublicKeyParts>(
}

/// Given an m and and unblinding factor, unblind the m.
fn unblind(key: &impl PublicKeyParts, m: &BigUint, unblinder: &BigUint) -> BigUint {
(m * unblinder) % key.n()
fn unblind(key: &impl PublicKeyPartsNew, m: &BoxedUint, unblinder: &BoxedUint) -> BoxedUint {
m.mul_mod(unblinder, key.n())
}

/// The following (deterministic) algorithm also recovers the prime factors `p` and `q` of a modulus `n`, given the
Expand Down Expand Up @@ -326,99 +325,6 @@ pub(crate) fn compute_private_exponent_carmicheal(
}
}

fn blind_new<R: CryptoRngCore, K: PublicKeyPartsNew>(
rng: &mut R,
key: &K,
c: &BoxedUint,
n_params: &BoxedResidueParams,
) -> (BoxedUint, BoxedUint) {
let mut r: BoxedUint;
let mut ir: CtOption<BoxedUint>;
let unblinder;
loop {
// TODO: use constant time gen
r = to_uint(rng.gen_biguint_below(&to_biguint(&key.n())));
// TODO: correct mapping
if r.is_zero().into() {
r = BoxedUint::one();
}
ir = r.inv_mod(key.n());

// TODO: constant time?
if let Some(ir) = ir.into() {
unblinder = ir;
break;
}
}

let c = {
let r = reduce(&r, n_params.clone());
let mut rpowe = r.pow(key.e()).retrieve();

let c = c.wrapping_mul(&rpowe);
let c = c.rem_vartime(key.n());

rpowe.zeroize();

c
};

(c, unblinder)
}

fn unblind_new(key: &impl PublicKeyPartsNew, m: &BoxedUint, unblinder: &BoxedUint) -> BoxedUint {
let a = m.wrapping_mul(unblinder);
a.rem_vartime(key.n())
}

pub fn rsa_decrypt_new<R: CryptoRngCore + ?Sized>(
mut rng: Option<&mut R>,
priv_key: &impl PrivateKeyPartsNew,
c: &BigUint,
) -> Result<BigUint> {
// convert to crypto bigint
let c = to_uint(c.clone());
let n = priv_key.n();
let d = priv_key.d();

if c >= **n {
return Err(Error::Decryption);
}

// TODO: is this fine?
if n.is_zero().into() {
return Err(Error::Decryption);
}

let mut ir = None;

let n_params = priv_key
.residue_params()
.cloned()
.unwrap_or_else(|| BoxedResidueParams::new(n.clone().get()).unwrap());

let c = if let Some(ref mut rng) = rng {
let (blinded, unblinder) = blind_new(rng, priv_key, &c, &n_params);
ir = Some(unblinder);
blinded
} else {
c
};

// TODO: fast path with precalculated values;
let c = reduce(&c, n_params);
let m = c.pow(&d).retrieve();

match ir {
Some(ref ir) => {
// unblind
let m = unblind_new(priv_key, &m, ir);
Ok(to_biguint(&m))
}
None => Ok(to_biguint(&m)),
}
}

#[cfg(test)]
mod tests {
use num_traits::FromPrimitive;
Expand Down
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