/* * * Copyright (c) 2020-2022 Project CHIP Authors * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ use alloc::sync::Arc; use core::ops::{Mul, Sub}; use crate::error::Error; use byteorder::{ByteOrder, LittleEndian}; use log::error; use mbedtls::{ bignum::Mpi, ecp::EcPoint, hash::Md, pk::{EcGroup, EcGroupId, Pk}, rng::{CtrDrbg, OsEntropy}, }; extern crate alloc; const MATTER_M_BIN: [u8; 65] = [ 0x04, 0x88, 0x6e, 0x2f, 0x97, 0xac, 0xe4, 0x6e, 0x55, 0xba, 0x9d, 0xd7, 0x24, 0x25, 0x79, 0xf2, 0x99, 0x3b, 0x64, 0xe1, 0x6e, 0xf3, 0xdc, 0xab, 0x95, 0xaf, 0xd4, 0x97, 0x33, 0x3d, 0x8f, 0xa1, 0x2f, 0x5f, 0xf3, 0x55, 0x16, 0x3e, 0x43, 0xce, 0x22, 0x4e, 0x0b, 0x0e, 0x65, 0xff, 0x02, 0xac, 0x8e, 0x5c, 0x7b, 0xe0, 0x94, 0x19, 0xc7, 0x85, 0xe0, 0xca, 0x54, 0x7d, 0x55, 0xa1, 0x2e, 0x2d, 0x20, ]; const MATTER_N_BIN: [u8; 65] = [ 0x04, 0xd8, 0xbb, 0xd6, 0xc6, 0x39, 0xc6, 0x29, 0x37, 0xb0, 0x4d, 0x99, 0x7f, 0x38, 0xc3, 0x77, 0x07, 0x19, 0xc6, 0x29, 0xd7, 0x01, 0x4d, 0x49, 0xa2, 0x4b, 0x4f, 0x98, 0xba, 0xa1, 0x29, 0x2b, 0x49, 0x07, 0xd6, 0x0a, 0xa6, 0xbf, 0xad, 0xe4, 0x50, 0x08, 0xa6, 0x36, 0x33, 0x7f, 0x51, 0x68, 0xc6, 0x4d, 0x9b, 0xd3, 0x60, 0x34, 0x80, 0x8c, 0xd5, 0x64, 0x49, 0x0b, 0x1e, 0x65, 0x6e, 0xdb, 0xe7, ]; #[allow(non_snake_case)] pub struct CryptoSpake2 { group: EcGroup, order: Mpi, xy: Mpi, w0: Mpi, w1: Mpi, M: EcPoint, N: EcPoint, L: EcPoint, pB: EcPoint, } impl CryptoSpake2 { #[allow(non_snake_case)] pub fn new() -> Result { let group = EcGroup::new(mbedtls::pk::EcGroupId::SecP256R1)?; let order = group.order()?; let M = EcPoint::from_binary(&group, &MATTER_M_BIN)?; let N = EcPoint::from_binary(&group, &MATTER_N_BIN)?; Ok(Self { group, order, xy: Mpi::new(0)?, M, N, w0: Mpi::new(0)?, w1: Mpi::new(0)?, L: EcPoint::new()?, pB: EcPoint::new()?, }) } // Computes w0 from w0s respectively pub fn set_w0_from_w0s(&mut self, w0s: &[u8]) -> Result<(), Error> { // From the Matter Spec, // w0 = w0s mod p // where p is the order of the curve self.w0 = Mpi::from_binary(w0s)?; self.w0 = self.w0.modulo(&self.order)?; Ok(()) } pub fn set_w1_from_w1s(&mut self, w1s: &[u8]) -> Result<(), Error> { // From the Matter Spec, // w1 = w1s mod p // where p is the order of the curve self.w1 = Mpi::from_binary(w1s)?; self.w1 = self.w1.modulo(&self.order)?; Ok(()) } pub fn set_w0(&mut self, w0: &[u8]) -> Result<(), Error> { self.w0 = Mpi::from_binary(w0)?; Ok(()) } pub fn set_w1(&mut self, w1: &[u8]) -> Result<(), Error> { self.w1 = Mpi::from_binary(w1)?; Ok(()) } #[allow(non_snake_case)] pub fn set_L(&mut self, l: &[u8]) -> Result<(), Error> { self.L = EcPoint::from_binary(&self.group, l)?; Ok(()) } #[allow(non_snake_case)] #[allow(dead_code)] pub fn set_L_from_w1s(&mut self, w1s: &[u8]) -> Result<(), Error> { // From the Matter spec, // L = w1 * P // where P is the generator of the underlying elliptic curve self.set_w1_from_w1s(w1s)?; // TODO: rust-mbedtls doesn't yet accept the DRBG parameter self.L = self.group.generator()?.mul(&mut self.group, &self.w1)?; Ok(()) } #[allow(non_snake_case)] pub fn get_pB(&mut self, pB: &mut [u8]) -> Result<(), Error> { // From the SPAKE2+ spec (https://datatracker.ietf.org/doc/draft-bar-cfrg-spake2plus/) // for y // - select random y between 0 to p // - Y = y*P + w0*N // - pB = Y // A private key on this curve is a random number between 0 to p let mut ctr_drbg = CtrDrbg::new(Arc::new(OsEntropy::new()), None)?; self.xy = Pk::generate_ec(&mut ctr_drbg, EcGroupId::SecP256R1)?.ec_private()?; let P = self.group.generator()?; self.pB = EcPoint::muladd(&mut self.group, &P, &self.xy, &self.N, &self.w0)?; let pB_internal = self.pB.to_binary(&self.group, false)?; let pB_internal = pB_internal.as_slice(); if pB_internal.len() != pB.len() { error!("pB length mismatch"); return Err(Error::Invalid); } pB.copy_from_slice(pB_internal); Ok(()) } #[allow(non_snake_case)] pub fn get_TT_as_verifier( &mut self, context: &[u8], pA: &[u8], pB: &[u8], out: &mut [u8], ) -> Result<(), Error> { let mut TT = Md::new(mbedtls::hash::Type::Sha256)?; // context Self::add_to_tt(&mut TT, context)?; // 2 empty identifiers Self::add_to_tt(&mut TT, &[])?; Self::add_to_tt(&mut TT, &[])?; // M Self::add_to_tt(&mut TT, &MATTER_M_BIN)?; // N Self::add_to_tt(&mut TT, &MATTER_N_BIN)?; // X = pA Self::add_to_tt(&mut TT, pA)?; // Y = pB Self::add_to_tt(&mut TT, pB)?; let X = EcPoint::from_binary(&self.group, pA)?; let (Z, V) = Self::get_ZV_as_verifier( &self.w0, &self.L, &mut self.M, &X, &self.xy, &self.order, &mut self.group, )?; // Z let tmp = Z.to_binary(&self.group, false)?; let tmp = tmp.as_slice(); Self::add_to_tt(&mut TT, tmp)?; // V let tmp = V.to_binary(&self.group, false)?; let tmp = tmp.as_slice(); Self::add_to_tt(&mut TT, tmp)?; // w0 let tmp = self.w0.to_binary()?; let tmp = tmp.as_slice(); Self::add_to_tt(&mut TT, tmp)?; TT.finish(out)?; Ok(()) } fn add_to_tt(tt: &mut Md, buf: &[u8]) -> Result<(), Error> { let mut len_buf: [u8; 8] = [0; 8]; LittleEndian::write_u64(&mut len_buf, buf.len() as u64); tt.update(&len_buf)?; if !buf.is_empty() { tt.update(buf)?; } Ok(()) } #[inline(always)] #[allow(non_snake_case)] #[allow(dead_code)] fn get_ZV_as_prover( w0: &Mpi, w1: &Mpi, N: &mut EcPoint, Y: &EcPoint, x: &Mpi, order: &Mpi, group: &mut EcGroup, ) -> Result<(EcPoint, EcPoint), Error> { // As per the RFC, the operation here is: // Z = h*x*(Y - w0*N) // V = h*w1*(Y - w0*N) // We will follow the same sequence as in C++ SDK, under the assumption // that the same sequence works for all embedded platforms. So the step // of operations is: // tmp = x*w0 // Z = x*Y + tmp*N (N is inverted to get the 'negative' effect) // Z = h*Z (cofactor Mul) let mut tmp = x.mul(w0)?; tmp = tmp.modulo(order)?; let inverted_N = Self::invert(group, N)?; let Z = EcPoint::muladd(group, Y, x, &inverted_N, &tmp)?; // Cofactor for P256 is 1, so that is a No-Op let mut tmp = w0.mul(w1)?; tmp = tmp.modulo(order)?; let V = EcPoint::muladd(group, Y, w1, &inverted_N, &tmp)?; Ok((Z, V)) } #[inline(always)] #[allow(non_snake_case)] #[allow(dead_code)] fn get_ZV_as_verifier( w0: &Mpi, L: &EcPoint, M: &mut EcPoint, X: &EcPoint, y: &Mpi, order: &Mpi, group: &mut EcGroup, ) -> Result<(EcPoint, EcPoint), Error> { // As per the RFC, the operation here is: // Z = h*y*(X - w0*M) // V = h*y*L // We will follow the same sequence as in C++ SDK, under the assumption // that the same sequence works for all embedded platforms. So the step // of operations is: // tmp = y*w0 // Z = y*X + tmp*M (M is inverted to get the 'negative' effect) // Z = h*Z (cofactor Mul) let mut tmp = y.mul(w0)?; tmp = tmp.modulo(order)?; let inverted_M = Self::invert(group, M)?; let Z = EcPoint::muladd(group, X, y, &inverted_M, &tmp)?; // Cofactor for P256 is 1, so that is a No-Op let V = L.mul(group, y)?; Ok((Z, V)) } fn invert(group: &mut EcGroup, num: &EcPoint) -> Result { let p = group.p()?; let num_y = num.y()?; let inverted_num_y = p.sub(&num_y)?; EcPoint::from_components(num.x()?, inverted_num_y) } } #[cfg(test)] mod tests { use super::CryptoSpake2; use crate::secure_channel::spake2p_test_vectors::test_vectors::*; use mbedtls::bignum::Mpi; use mbedtls::ecp::EcPoint; #[test] #[allow(non_snake_case)] fn test_get_X() { for t in RFC_T { let mut c = CryptoSpake2::new().unwrap(); let x = Mpi::from_binary(&t.x).unwrap(); c.set_w0(&t.w0).unwrap(); let P = c.group.generator().unwrap(); let r = EcPoint::muladd(&mut c.group, &P, &x, &c.M, &c.w0).unwrap(); assert_eq!(t.X, r.to_binary(&c.group, false).unwrap().as_slice()); } } #[test] #[allow(non_snake_case)] fn test_get_Y() { for t in RFC_T { let mut c = CryptoSpake2::new().unwrap(); let y = Mpi::from_binary(&t.y).unwrap(); c.set_w0(&t.w0).unwrap(); let P = c.group.generator().unwrap(); let r = EcPoint::muladd(&mut c.group, &P, &y, &c.N, &c.w0).unwrap(); assert_eq!(t.Y, r.to_binary(&c.group, false).unwrap().as_slice()); } } #[test] #[allow(non_snake_case)] fn test_get_ZV_as_prover() { for t in RFC_T { let mut c = CryptoSpake2::new().unwrap(); let x = Mpi::from_binary(&t.x).unwrap(); c.set_w0(&t.w0).unwrap(); c.set_w1(&t.w1).unwrap(); let Y = EcPoint::from_binary(&c.group, &t.Y).unwrap(); let (Z, V) = CryptoSpake2::get_ZV_as_prover( &c.w0, &c.w1, &mut c.N, &Y, &x, &c.order, &mut c.group, ) .unwrap(); assert_eq!(t.Z, Z.to_binary(&c.group, false).unwrap().as_slice()); assert_eq!(t.V, V.to_binary(&c.group, false).unwrap().as_slice()); } } #[test] #[allow(non_snake_case)] fn test_get_ZV_as_verifier() { for t in RFC_T { let mut c = CryptoSpake2::new().unwrap(); let y = Mpi::from_binary(&t.y).unwrap(); c.set_w0(&t.w0).unwrap(); let X = EcPoint::from_binary(&c.group, &t.X).unwrap(); let L = EcPoint::from_binary(&c.group, &t.L).unwrap(); let (Z, V) = CryptoSpake2::get_ZV_as_verifier( &c.w0, &L, &mut c.M, &X, &y, &c.order, &mut c.group, ) .unwrap(); assert_eq!(t.Z, Z.to_binary(&c.group, false).unwrap().as_slice()); assert_eq!(t.V, V.to_binary(&c.group, false).unwrap().as_slice()); } } }