-//! An implementation of the [SPAKE2][1] password-authenticated key-exchange
-//! algorithm
-//!
-//! This library implements the SPAKE2 password-authenticated key exchange
-//! ("PAKE") algorithm. This allows two parties, who share a weak password, to
-//! safely derive a strong shared secret (and therefore build an
-//! encrypted+authenticated channel).
-//!
-//! A passive attacker who eavesdrops on the connection learns no information
-//! about the password or the generated secret. An active attacker
-//! (man-in-the-middle) gets exactly one guess at the password, and unless they
-//! get it right, they learn no information about the password or the generated
-//! secret. Each execution of the protocol enables one guess. The use of a weak
-//! password is made safer by the rate-limiting of guesses: no off-line
-//! dictionary attack is available to the network-level attacker, and the
-//! protocol does not depend upon having previously-established confidentiality
-//! of the network (unlike e.g. sending a plaintext password over TLS).
-//!
-//! The protocol requires the exchange of one pair of messages, so only one round
-//! trip is necessary to establish the session key. If key-confirmation is
-//! necessary, that will require a second round trip.
-//!
-//! All messages are bytestrings. For the default security level (using the
-//! Ed25519 elliptic curve, roughly equivalent to an 128-bit symmetric key), the
-//! message is 33 bytes long.
-//!
-//! This implementation is generic over a `Group`, which defines the cyclic
-//! group to use, the functions which convert group elements and scalars to
-//! and from bytestrings, and the three distinctive group elements used in
-//! the blinding process. Only one such Group is implemented, named
-//! `Ed25519Group`, which provides fast operations and high security, and is
-//! compatible with my [python
-//! implementation](https://github.com/warner/python-spake2).
-//!
-//! # What Is It Good For?
-//!
-//! PAKE can be used in a pairing protocol, like the initial version of Firefox
-//! Sync (the one with J-PAKE), to introduce one device to another and help them
-//! share secrets. In this mode, one device creates a random code, the user
-//! copies that code to the second device, then both devices use the code as a
-//! one-time password and run the PAKE protocol. Once both devices have a shared
-//! strong key, they can exchange other secrets safely.
-//!
-//! PAKE can also be used (carefully) in a login protocol, where SRP is perhaps
-//! the best-known approach. Traditional non-PAKE login consists of sending a
-//! plaintext password through a TLS-encrypted channel, to a server which then
-//! checks it (by hashing/stretching and comparing against a stored verifier). In
-//! a PAKE login, both sides put the password into their PAKE protocol, and then
-//! confirm that their generated key is the same. This nominally does not require
-//! the initial TLS-protected channel. However note that it requires other,
-//! deeper design considerations (the PAKE protocol must be bound to whatever
-//! protected channel you end up using, else the attacker can wait for PAKE to
-//! complete normally and then steal the channel), and is not simply a drop-in
-//! replacement. In addition, the server cannot hash/stretch the password very
-//! much (see the note on "Augmented PAKE" below), so unless the client is
-//! willing to perform key-stretching before running PAKE, the server's stored
-//! verifier will be vulnerable to a low-cost dictionary attack.
-//!
+#![no_std]
+#![cfg_attr(docsrs, feature(doc_cfg))]
+#![doc = include_str!("../README.md")]
+#![doc(
+ html_logo_url = "https://raw.githubusercontent.com/RustCrypto/meta/master/logo.svg",
+ html_favicon_url = "https://raw.githubusercontent.com/RustCrypto/meta/master/logo.svg"
+)]
+#![forbid(unsafe_code)]
+#![warn(missing_docs, rust_2018_idioms, unused_qualifications)]
+
//! # Usage
//!
-//! Add the `spake2 dependency to your `Cargo.toml`:
-//!
-//! ```toml
-//! [dependencies]
-//! spake2 = "0.1"
-//! ```
-//!
-//! and this to your crate root:
-//!
-//! ```rust
-//! extern crate spake2;
-//! ```
-//!
-//!
//! Alice and Bob both initialize their SPAKE2 instances with the same (weak)
//! password. They will exchange messages to (hopefully) derive a shared secret
//! key. The protocol is symmetric: for each operation that Alice does, Bob will
//! Thus a client-side program start with:
//!
//! ```rust
-//! use spake2::{Ed25519Group, Identity, Password, SPAKE2};
+//! use spake2::{Ed25519Group, Identity, Password, Spake2};
//! # fn send(msg: &[u8]) {}
-//! let (s1, outbound_msg) = SPAKE2::<Ed25519Group>::start_a(
+//! let (s1, outbound_msg) = Spake2::<Ed25519Group>::start_a(
//! &Password::new(b"password"),
//! &Identity::new(b"client id string"),
//! &Identity::new(b"server id string"));
//! send(&outbound_msg);
//!
-//! # fn receive() -> Vec<u8> { let (s2, i2) = SPAKE2::<Ed25519Group>::start_b(&Password::new(b"password"), &Identity::new(b"client id string"), &Identity::new(b"server id string")); i2 }
+//! # fn receive() -> Vec<u8> { let (s2, i2) = Spake2::<Ed25519Group>::start_b(&Password::new(b"password"), &Identity::new(b"client id string"), &Identity::new(b"server id string")); i2 }
//! let inbound_msg = receive();
//! let key1 = s1.finish(&inbound_msg).unwrap();
//! ```
//!
//! ```rust
//! # fn send(msg: &[u8]) {}
-//! use spake2::{Ed25519Group, Identity, Password, SPAKE2};
-//! let (s1, outbound_msg) = SPAKE2::<Ed25519Group>::start_b(
+//! use spake2::{Ed25519Group, Identity, Password, Spake2};
+//! let (s1, outbound_msg) = Spake2::<Ed25519Group>::start_b(
//! &Password::new(b"password"),
//! &Identity::new(b"client id string"),
//! &Identity::new(b"server id string"));
//! send(&outbound_msg);
//!
-//! # fn receive() -> Vec<u8> { let (s2, i2) = SPAKE2::<Ed25519Group>::start_a(&Password::new(b"password"), &Identity::new(b"client id string"), &Identity::new(b"server id string")); i2 }
+//! # fn receive() -> Vec<u8> { let (s2, i2) = Spake2::<Ed25519Group>::start_a(&Password::new(b"password"), &Identity::new(b"client id string"), &Identity::new(b"server id string")); i2 }
//! let inbound_msg = receive();
//! let key2 = s1.finish(&inbound_msg).unwrap();
//! ```
//!
//! The shared key can be used as an HMAC key to provide data integrity on
//! subsequent messages, or as an authenticated-encryption key (e.g.
-//! nacl.secretbox). It can also be fed into [HKDF] [1] to derive other
+//! nacl.secretbox). It can also be fed into [HKDF][1] to derive other
//! session keys as necessary.
//!
//! The `SPAKE2` instances, and the messages they create, are single-use. Create
//!
//! ```rust
//! # fn send(msg: &[u8]) {}
-//! use spake2::{Ed25519Group, Identity, Password, SPAKE2};
-//! let (s1, outbound_msg) = SPAKE2::<Ed25519Group>::start_symmetric(
+//! use spake2::{Ed25519Group, Identity, Password, Spake2};
+//! let (s1, outbound_msg) = Spake2::<Ed25519Group>::start_symmetric(
//! &Password::new(b"password"),
//! &Identity::new(b"shared id string"));
//! send(&outbound_msg);
//!
-//! # fn receive() -> Vec<u8> { let (s2, i2) = SPAKE2::<Ed25519Group>::start_symmetric(&Password::new(b"password"), &Identity::new(b"shared id string")); i2 }
+//! # fn receive() -> Vec<u8> { let (s2, i2) = Spake2::<Ed25519Group>::start_symmetric(&Password::new(b"password"), &Identity::new(b"shared id string")); i2 }
//! let inbound_msg = receive();
//! let key1 = s1.finish(&inbound_msg).unwrap();
//! ```
//!
//! ```rust
//! # fn send(msg: &[u8]) {}
-//! use spake2::{Ed25519Group, Identity, Password, SPAKE2};
-//! let (s1, outbound_msg) = SPAKE2::<Ed25519Group>::start_symmetric(
+//! use spake2::{Ed25519Group, Identity, Password, Spake2};
+//! let (s1, outbound_msg) = Spake2::<Ed25519Group>::start_symmetric(
//! &Password::new(b"password"),
//! &Identity::new(b"shared id string"));
//! send(&outbound_msg);
//!
-//! # fn receive() -> Vec<u8> { let (s2, i2) = SPAKE2::<Ed25519Group>::start_symmetric(&Password::new(b"password"), &Identity::new(b"shared id string")); i2 }
+//! # fn receive() -> Vec<u8> { let (s2, i2) = Spake2::<Ed25519Group>::start_symmetric(&Password::new(b"password"), &Identity::new(b"shared id string")); i2 }
//! let inbound_msg = receive();
//! let key1 = s1.finish(&inbound_msg).unwrap();
//! ```
//! [6]: http://eprint.iacr.org/2003/038.pdf "Pretty-Simple Password-Authenticated Key-Exchange Under Standard Assumptions"
//! [7]: https://moderncrypto.org/mail-archive/curves/2015/000419.html "PAKE questions"
-#![doc(html_logo_url = "https://raw.githubusercontent.com/RustCrypto/meta/master/logo_small.png")]
-#![deny(warnings)]
-#![forbid(unsafe_code)]
+#[allow(unused_imports)]
+#[macro_use]
+extern crate alloc;
-extern crate curve25519_dalek;
-extern crate hex;
-extern crate hkdf;
-extern crate num_bigint;
-extern crate rand;
-extern crate sha2;
+#[cfg(feature = "std")]
+#[cfg_attr(test, macro_use)]
+extern crate std;
-use curve25519_dalek::constants::ED25519_BASEPOINT_POINT;
-use curve25519_dalek::edwards::CompressedEdwardsY;
-use curve25519_dalek::edwards::EdwardsPoint as c2_Element;
-use curve25519_dalek::scalar::Scalar as c2_Scalar;
+mod ed25519;
+mod error;
+mod group;
-use hkdf::Hkdf;
-use rand::{rngs::OsRng, CryptoRng, Rng};
-use sha2::{Digest, Sha256};
-use std::fmt;
-use std::ops::Deref;
+pub use self::{
+ ed25519::Ed25519Group,
+ error::{Error, Result},
+ group::Group,
+};
-/* "newtype pattern": it's a Vec<u8>, but only used for a specific argument
- * type, to distinguish between ones that are meant as passwords, and ones
- * that are meant as identity strings */
+use alloc::vec::Vec;
+use core::{fmt, ops::Deref, str};
+use curve25519_dalek::{edwards::EdwardsPoint as c2_Element, scalar::Scalar as c2_Scalar};
+use rand_core::{CryptoRng, RngCore};
+#[cfg(feature = "getrandom")]
+use rand_core::OsRng;
+
+/// Password type.
+// TODO(tarcieri): avoid allocation?
#[derive(PartialEq, Eq, Clone)]
pub struct Password(Vec<u8>);
+
impl Password {
- pub fn new(p: &[u8]) -> Password {
- Password(p.to_vec())
+ /// Create a new password.
+ pub fn new(p: impl AsRef<[u8]>) -> Password {
+ Password(p.as_ref().to_vec())
}
}
+
impl Deref for Password {
type Target = Vec<u8>;
+
fn deref(&self) -> &Vec<u8> {
&self.0
}
}
+/// SPAKE2 identity.
+// TODO(tarcieri): avoid allocation?
#[derive(PartialEq, Eq, Clone)]
pub struct Identity(Vec<u8>);
+
impl Deref for Identity {
type Target = Vec<u8>;
+
fn deref(&self) -> &Vec<u8> {
&self.0
}
}
+
impl Identity {
+ /// Create a new identity.
pub fn new(p: &[u8]) -> Identity {
Identity(p.to_vec())
}
}
+/// Session type identifying the "side" in a SPAKE2 exchange.
#[derive(Debug, PartialEq, Eq)]
-pub enum ErrorType {
- BadSide,
- WrongLength,
- CorruptMessage,
-}
-
-#[derive(Debug, PartialEq, Eq)]
-pub struct SPAKEErr {
- pub kind: ErrorType,
+enum Side {
+ A,
+ B,
+ Symmetric,
}
-pub trait Group {
- type Scalar;
- type Element;
- //type Element: Add<Output=Self::Element>
- // + Mul<Self::Scalar, Output=Self::Element>;
- // const element_length: usize; // in unstable, or u8
- //type ElementBytes : Index<usize, Output=u8>+IndexMut<usize>; // later
- type TranscriptHash;
- fn name() -> &'static str;
- fn const_m() -> Self::Element;
- fn const_n() -> Self::Element;
- fn const_s() -> Self::Element;
- fn hash_to_scalar(s: &[u8]) -> Self::Scalar;
- fn random_scalar<T>(cspring: &mut T) -> Self::Scalar
- where
- T: Rng + CryptoRng;
- fn scalar_neg(s: &Self::Scalar) -> Self::Scalar;
- fn element_to_bytes(e: &Self::Element) -> Vec<u8>;
- fn bytes_to_element(b: &[u8]) -> Option<Self::Element>;
- fn element_length() -> usize;
- fn basepoint_mult(s: &Self::Scalar) -> Self::Element;
- fn scalarmult(e: &Self::Element, s: &Self::Scalar) -> Self::Element;
- fn add(a: &Self::Element, b: &Self::Element) -> Self::Element;
+/// SPAKE2 algorithm.
+#[derive(Eq, PartialEq)]
+pub struct Spake2<G: Group> {
+ //where &G::Scalar: Neg {
+ side: Side,
+ xy_scalar: G::Scalar,
+ password_vec: Vec<u8>,
+ id_a: Vec<u8>,
+ id_b: Vec<u8>,
+ id_s: Vec<u8>,
+ msg1: Vec<u8>,
+ password_scalar: G::Scalar,
}
-#[derive(Debug, PartialEq, Eq)]
-pub struct Ed25519Group;
-
-impl Group for Ed25519Group {
- type Scalar = c2_Scalar;
- type Element = c2_Element;
- //type ElementBytes = Vec<u8>;
- //type ElementBytes = [u8; 32];
- //type ScalarBytes
- type TranscriptHash = Sha256;
-
- fn name() -> &'static str {
- "Ed25519"
- }
-
- fn const_m() -> c2_Element {
- // python -c "import binascii, spake2; b=binascii.hexlify(spake2.ParamsEd25519.M.to_bytes()); print(', '.join(['0x'+b[i:i+2] for i in range(0,len(b),2)]))"
- // 15cfd18e385952982b6a8f8c7854963b58e34388c8e6dae891db756481a02312
- CompressedEdwardsY([
- 0x15, 0xcf, 0xd1, 0x8e, 0x38, 0x59, 0x52, 0x98, 0x2b, 0x6a, 0x8f, 0x8c, 0x78, 0x54,
- 0x96, 0x3b, 0x58, 0xe3, 0x43, 0x88, 0xc8, 0xe6, 0xda, 0xe8, 0x91, 0xdb, 0x75, 0x64,
- 0x81, 0xa0, 0x23, 0x12,
- ])
- .decompress()
- .unwrap()
+impl<G: Group> Spake2<G> {
+ /// Start with identity `idA`.
+ ///
+ /// Uses the system RNG.
+ #[cfg(feature = "getrandom")]
+ #[cfg_attr(docsrs, doc(cfg(feature = "getrandom")))]
+ pub fn start_a(password: &Password, id_a: &Identity, id_b: &Identity) -> (Spake2<G>, Vec<u8>) {
+ Self::start_a_with_rng(password, id_a, id_b, OsRng)
}
- fn const_n() -> c2_Element {
- // python -c "import binascii, spake2; b=binascii.hexlify(spake2.ParamsEd25519.N.to_bytes()); print(', '.join(['0x'+b[i:i+2] for i in range(0,len(b),2)]))"
- // f04f2e7eb734b2a8f8b472eaf9c3c632576ac64aea650b496a8a20ff00e583c3
- CompressedEdwardsY([
- 0xf0, 0x4f, 0x2e, 0x7e, 0xb7, 0x34, 0xb2, 0xa8, 0xf8, 0xb4, 0x72, 0xea, 0xf9, 0xc3,
- 0xc6, 0x32, 0x57, 0x6a, 0xc6, 0x4a, 0xea, 0x65, 0x0b, 0x49, 0x6a, 0x8a, 0x20, 0xff,
- 0x00, 0xe5, 0x83, 0xc3,
- ])
- .decompress()
- .unwrap()
+ /// Start with identity `idB`.
+ ///
+ /// Uses the system RNG.
+ #[cfg(feature = "getrandom")]
+ #[cfg_attr(docsrs, doc(cfg(feature = "getrandom")))]
+ pub fn start_b(password: &Password, id_a: &Identity, id_b: &Identity) -> (Spake2<G>, Vec<u8>) {
+ Self::start_b_with_rng(password, id_a, id_b, OsRng)
}
- fn const_s() -> c2_Element {
- // python -c "import binascii, spake2; b=binascii.hexlify(spake2.ParamsEd25519.S.to_bytes()); print(', '.join(['0x'+b[i:i+2] for i in range(0,len(b),2)]))"
- // 6f00dae87c1be1a73b5922ef431cd8f57879569c222d22b1cd71e8546ab8e6f1
- CompressedEdwardsY([
- 0x6f, 0x00, 0xda, 0xe8, 0x7c, 0x1b, 0xe1, 0xa7, 0x3b, 0x59, 0x22, 0xef, 0x43, 0x1c,
- 0xd8, 0xf5, 0x78, 0x79, 0x56, 0x9c, 0x22, 0x2d, 0x22, 0xb1, 0xcd, 0x71, 0xe8, 0x54,
- 0x6a, 0xb8, 0xe6, 0xf1,
- ])
- .decompress()
- .unwrap()
+ /// Start with symmetric identity.
+ ///
+ /// Uses the system RNG.
+ #[cfg(feature = "getrandom")]
+ #[cfg_attr(docsrs, doc(cfg(feature = "getrandom")))]
+ pub fn start_symmetric(password: &Password, id_s: &Identity) -> (Spake2<G>, Vec<u8>) {
+ Self::start_symmetric_with_rng(password, id_s, OsRng)
}
- fn hash_to_scalar(s: &[u8]) -> c2_Scalar {
- ed25519_hash_to_scalar(s)
- }
- fn random_scalar<T>(cspring: &mut T) -> c2_Scalar
- where
- T: Rng + CryptoRng,
- {
- c2_Scalar::random(cspring)
- }
- fn scalar_neg(s: &c2_Scalar) -> c2_Scalar {
- -s
- }
- fn element_to_bytes(s: &c2_Element) -> Vec<u8> {
- s.compress().as_bytes().to_vec()
- }
- fn element_length() -> usize {
- 32
- }
- fn bytes_to_element(b: &[u8]) -> Option<c2_Element> {
- if b.len() != 32 {
- return None;
- }
- //let mut bytes: [u8; 32] =
- let mut bytes = [0u8; 32];
- bytes.copy_from_slice(b);
- let cey = CompressedEdwardsY(bytes);
- // CompressedEdwardsY::new(b)
- cey.decompress()
+ /// Start with identity `idA` and the provided cryptographically secure RNG.
+ pub fn start_a_with_rng(
+ password: &Password,
+ id_a: &Identity,
+ id_b: &Identity,
+ mut csrng: impl CryptoRng + RngCore,
+ ) -> (Spake2<G>, Vec<u8>) {
+ let xy_scalar: G::Scalar = G::random_scalar(&mut csrng);
+ Self::start_a_internal(password, id_a, id_b, xy_scalar)
}
- fn basepoint_mult(s: &c2_Scalar) -> c2_Element {
- //c2_Element::basepoint_mult(s)
- ED25519_BASEPOINT_POINT * s
- }
- fn scalarmult(e: &c2_Element, s: &c2_Scalar) -> c2_Element {
- e * s
- //e.scalar_mult(s)
- }
- fn add(a: &c2_Element, b: &c2_Element) -> c2_Element {
- a + b
- //a.add(b)
+ /// Start with identity `idB` and the provided cryptographically secure RNG.
+ pub fn start_b_with_rng(
+ password: &Password,
+ id_a: &Identity,
+ id_b: &Identity,
+ mut csrng: impl CryptoRng + RngCore,
+ ) -> (Spake2<G>, Vec<u8>) {
+ let xy_scalar: G::Scalar = G::random_scalar(&mut csrng);
+ Self::start_b_internal(password, id_a, id_b, xy_scalar)
}
-}
-fn ed25519_hash_to_scalar(s: &[u8]) -> c2_Scalar {
- //c2_Scalar::hash_from_bytes::<Sha512>(&s)
- // spake2.py does:
- // h = HKDF(salt=b"", ikm=s, hash=SHA256, info=b"SPAKE2 pw", len=32+16)
- // i = int(h, 16)
- // i % q
-
- let mut okm = [0u8; 32 + 16];
- Hkdf::<Sha256>::extract(Some(b""), s)
- .expand(b"SPAKE2 pw", &mut okm)
- .unwrap();
- //println!("expanded: {}{}", "................................", okm.iter().to_hex()); // ok
-
- let mut reducible = [0u8; 64]; // little-endian
- for (i, x) in okm.iter().enumerate().take(32 + 16) {
- reducible[32 + 16 - 1 - i] = *x;
+ /// Start with symmetric identity and the provided cryptographically secure RNG.
+ pub fn start_symmetric_with_rng(
+ password: &Password,
+ id_s: &Identity,
+ mut csrng: impl CryptoRng + RngCore,
+ ) -> (Spake2<G>, Vec<u8>) {
+ let xy_scalar: G::Scalar = G::random_scalar(&mut csrng);
+ Self::start_symmetric_internal(password, id_s, xy_scalar)
}
- //println!("reducible: {}", reducible.iter().to_hex());
- c2_Scalar::from_bytes_mod_order_wide(&reducible)
- //let reduced = c2_Scalar::reduce(&reducible);
- //println!("reduced: {}", reduced.as_bytes().to_hex());
- //println!("done");
- //reduced
-}
-fn ed25519_hash_ab(
- password_vec: &[u8],
- id_a: &[u8],
- id_b: &[u8],
- first_msg: &[u8],
- second_msg: &[u8],
- key_bytes: &[u8],
-) -> Vec<u8> {
- assert_eq!(first_msg.len(), 32);
- assert_eq!(second_msg.len(), 32);
- // the transcript is fixed-length, made up of 6 32-byte values:
- // byte 0-31 : sha256(pw)
- // byte 32-63 : sha256(idA)
- // byte 64-95 : sha256(idB)
- // byte 96-127 : X_msg
- // byte 128-159: Y_msg
- // byte 160-191: K_bytes
- let mut transcript = [0u8; 6 * 32];
-
- let mut pw_hash = Sha256::new();
- pw_hash.input(password_vec);
- transcript[0..32].copy_from_slice(&pw_hash.result());
-
- let mut ida_hash = Sha256::new();
- ida_hash.input(id_a);
- transcript[32..64].copy_from_slice(&ida_hash.result());
-
- let mut idb_hash = Sha256::new();
- idb_hash.input(id_b);
- transcript[64..96].copy_from_slice(&idb_hash.result());
-
- transcript[96..128].copy_from_slice(first_msg);
- transcript[128..160].copy_from_slice(second_msg);
- transcript[160..192].copy_from_slice(key_bytes);
-
- //println!("transcript: {:?}", transcript.iter().to_hex());
-
- //let mut hash = G::TranscriptHash::default();
- let mut hash = Sha256::new();
- hash.input(transcript.to_vec());
- hash.result().to_vec()
-}
+ /// Finish SPAKE2.
+ pub fn finish(self, msg2: &[u8]) -> Result<Vec<u8>> {
+ if msg2.len() != 1 + G::element_length() {
+ return Err(Error::WrongLength);
+ }
+ let msg_side = msg2[0];
-fn ed25519_hash_symmetric(
- password_vec: &[u8],
- id_s: &[u8],
- msg_u: &[u8],
- msg_v: &[u8],
- key_bytes: &[u8],
-) -> Vec<u8> {
- assert_eq!(msg_u.len(), 32);
- assert_eq!(msg_v.len(), 32);
- // # since we don't know which side is which, we must sort the messages
- // first_msg, second_msg = sorted([msg1, msg2])
- // transcript = b"".join([sha256(pw).digest(),
- // sha256(idSymmetric).digest(),
- // first_msg, second_msg, K_bytes])
-
- // the transcript is fixed-length, made up of 5 32-byte values:
- // byte 0-31 : sha256(pw)
- // byte 32-63 : sha256(idSymmetric)
- // byte 64-95 : X_msg
- // byte 96-127 : Y_msg
- // byte 128-159: K_bytes
- let mut transcript = [0u8; 5 * 32];
-
- let mut pw_hash = Sha256::new();
- pw_hash.input(password_vec);
- transcript[0..32].copy_from_slice(&pw_hash.result());
-
- let mut ids_hash = Sha256::new();
- ids_hash.input(id_s);
- transcript[32..64].copy_from_slice(&ids_hash.result());
-
- if msg_u < msg_v {
- transcript[64..96].copy_from_slice(msg_u);
- transcript[96..128].copy_from_slice(msg_v);
- } else {
- transcript[64..96].copy_from_slice(msg_v);
- transcript[96..128].copy_from_slice(msg_u);
- }
- transcript[128..160].copy_from_slice(key_bytes);
+ match self.side {
+ Side::A => match msg_side {
+ 0x42 => (), // 'B'
+ _ => return Err(Error::BadSide),
+ },
+ Side::B => match msg_side {
+ 0x41 => (), // 'A'
+ _ => return Err(Error::BadSide),
+ },
+ Side::Symmetric => match msg_side {
+ 0x53 => (), // 'S'
+ _ => return Err(Error::BadSide),
+ },
+ }
- let mut hash = Sha256::new();
- hash.input(transcript.to_vec());
- hash.result().to_vec()
-}
+ let msg2_element = match G::bytes_to_element(&msg2[1..]) {
+ Some(x) => x,
+ None => return Err(Error::CorruptMessage),
+ };
-/* "session type pattern" */
+ // a: K = (Y+N*(-pw))*x
+ // b: K = (X+M*(-pw))*y
+ let unblinding = match self.side {
+ Side::A => G::const_n(),
+ Side::B => G::const_m(),
+ Side::Symmetric => G::const_s(),
+ };
+ let tmp1 = G::scalarmult(&unblinding, &G::scalar_neg(&self.password_scalar));
+ let tmp2 = G::add(&msg2_element, &tmp1);
+ let key_element = G::scalarmult(&tmp2, &self.xy_scalar);
+ let key_bytes = G::element_to_bytes(&key_element);
-#[derive(Debug, PartialEq, Eq)]
-enum Side {
- A,
- B,
- Symmetric,
-}
+ // key = H(H(pw) + H(idA) + H(idB) + X + Y + K)
+ //transcript = b"".join([sha256(pw).digest(),
+ // sha256(idA).digest(), sha256(idB).digest(),
+ // X_msg, Y_msg, K_bytes])
+ //key = sha256(transcript).digest()
+ // note that both sides must use the same order
-// we implement a custom Debug below, to avoid revealing secrets in a dump
-#[derive(PartialEq, Eq)]
-pub struct SPAKE2<G: Group> {
- //where &G::Scalar: Neg {
- side: Side,
- xy_scalar: G::Scalar,
- password_vec: Vec<u8>,
- id_a: Vec<u8>,
- id_b: Vec<u8>,
- id_s: Vec<u8>,
- msg1: Vec<u8>,
- password_scalar: G::Scalar,
-}
+ Ok(match self.side {
+ Side::A => ed25519::hash_ab(
+ &self.password_vec,
+ &self.id_a,
+ &self.id_b,
+ self.msg1.as_slice(),
+ &msg2[1..],
+ &key_bytes,
+ ),
+ Side::B => ed25519::hash_ab(
+ &self.password_vec,
+ &self.id_a,
+ &self.id_b,
+ &msg2[1..],
+ self.msg1.as_slice(),
+ &key_bytes,
+ ),
+ Side::Symmetric => ed25519::hash_symmetric(
+ &self.password_vec,
+ &self.id_s,
+ &self.msg1,
+ &msg2[1..],
+ &key_bytes,
+ ),
+ })
+ }
-impl<G: Group> SPAKE2<G> {
fn start_internal(
side: Side,
password: &Password,
id_b: &Identity,
id_s: &Identity,
xy_scalar: G::Scalar,
- ) -> (SPAKE2<G>, Vec<u8>) {
+ ) -> (Spake2<G>, Vec<u8>) {
//let password_scalar: G::Scalar = hash_to_scalar::<G::Scalar>(password);
- let password_scalar: G::Scalar = G::hash_to_scalar(&password);
+ let password_scalar: G::Scalar = G::hash_to_scalar(password);
// a: X = B*x + M*pw
// b: Y = B*y + N*pw
//let m1: G::Element = &G::basepoint_mult(&x) + &(blinding * &password_scalar);
let msg1: Vec<u8> = G::element_to_bytes(&m1);
let mut password_vec = Vec::new();
- password_vec.extend_from_slice(&password);
+ password_vec.extend_from_slice(password);
let mut id_a_copy = Vec::new();
- id_a_copy.extend_from_slice(&id_a);
+ id_a_copy.extend_from_slice(id_a);
let mut id_b_copy = Vec::new();
- id_b_copy.extend_from_slice(&id_b);
+ id_b_copy.extend_from_slice(id_b);
let mut id_s_copy = Vec::new();
- id_s_copy.extend_from_slice(&id_s);
+ id_s_copy.extend_from_slice(id_s);
- let mut msg_and_side = Vec::new();
- msg_and_side.push(match side {
+ let mut msg_and_side = vec![match side {
Side::A => 0x41, // 'A'
Side::B => 0x42, // 'B'
Side::Symmetric => 0x53, // 'S'
- });
+ }];
msg_and_side.extend_from_slice(&msg1);
(
- SPAKE2 {
+ Spake2 {
side,
xy_scalar,
password_vec, // string
id_a: id_a_copy,
id_b: id_b_copy,
id_s: id_s_copy,
- msg1: msg1.clone(),
+ msg1,
password_scalar, // scalar
},
msg_and_side,
id_a: &Identity,
id_b: &Identity,
xy_scalar: G::Scalar,
- ) -> (SPAKE2<G>, Vec<u8>) {
+ ) -> (Spake2<G>, Vec<u8>) {
Self::start_internal(
Side::A,
- &password,
- &id_a,
- &id_b,
+ password,
+ id_a,
+ id_b,
&Identity::new(b""),
xy_scalar,
)
id_a: &Identity,
id_b: &Identity,
xy_scalar: G::Scalar,
- ) -> (SPAKE2<G>, Vec<u8>) {
+ ) -> (Spake2<G>, Vec<u8>) {
Self::start_internal(
Side::B,
- &password,
- &id_a,
- &id_b,
+ password,
+ id_a,
+ id_b,
&Identity::new(b""),
xy_scalar,
)
password: &Password,
id_s: &Identity,
xy_scalar: G::Scalar,
- ) -> (SPAKE2<G>, Vec<u8>) {
+ ) -> (Spake2<G>, Vec<u8>) {
Self::start_internal(
Side::Symmetric,
- &password,
+ password,
&Identity::new(b""),
&Identity::new(b""),
- &id_s,
+ id_s,
xy_scalar,
)
}
+}
- pub fn start_a(password: &Password, id_a: &Identity, id_b: &Identity) -> (SPAKE2<G>, Vec<u8>) {
- let mut cspring: OsRng = OsRng::new().unwrap();
- let xy_scalar: G::Scalar = G::random_scalar(&mut cspring);
- Self::start_a_internal(&password, &id_a, &id_b, xy_scalar)
+impl<G: Group> fmt::Debug for Spake2<G> {
+ fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+ fmt.debug_struct("SPAKE2")
+ .field("group", &G::name())
+ .field("side", &self.side)
+ .field("idA", &MaybeUtf8(&self.id_a))
+ .field("idB", &MaybeUtf8(&self.id_b))
+ .field("idS", &MaybeUtf8(&self.id_s))
+ .finish()
}
+}
+
+struct MaybeUtf8<'a>(&'a [u8]);
+
+impl fmt::Debug for MaybeUtf8<'_> {
+ fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+ if let Ok(s) = str::from_utf8(self.0) {
+ write!(fmt, "(s={})", s)
+ } else {
+ write!(fmt, "(hex=")?;
+
+ for byte in self.0 {
+ write!(fmt, "{:x}", byte)?;
+ }
- pub fn start_b(password: &Password, id_a: &Identity, id_b: &Identity) -> (SPAKE2<G>, Vec<u8>) {
- let mut cspring: OsRng = OsRng::new().unwrap();
- let xy_scalar: G::Scalar = G::random_scalar(&mut cspring);
- Self::start_b_internal(&password, &id_a, &id_b, xy_scalar)
+ write!(fmt, ")")
+ }
}
+}
- pub fn start_symmetric(password: &Password, id_s: &Identity) -> (SPAKE2<G>, Vec<u8>) {
- let mut cspring: OsRng = OsRng::new().unwrap();
- let xy_scalar: G::Scalar = G::random_scalar(&mut cspring);
- Self::start_symmetric_internal(&password, &id_s, xy_scalar)
+/// This compares results against the python compatibility tests:
+/// spake2.test.test_compat.SPAKE2.test_asymmetric . The python test passes a
+/// deterministic RNG (used only for tests, of course) into the per-Group
+/// "random_scalar()" function, which results in some particular scalar.
+#[cfg(all(test, feature = "std"))]
+mod tests {
+ use crate::*;
+ use curve25519_dalek::constants::ED25519_BASEPOINT_POINT;
+ use num_bigint::BigUint;
+
+ // the python tests show the long-integer form of scalars. the rust code
+ // wants an array of bytes (little-endian). Make sure the way we convert
+ // things works correctly.
+ fn decimal_to_scalar(d: &[u8]) -> c2_Scalar {
+ let bytes = BigUint::parse_bytes(d, 10).unwrap().to_bytes_le();
+ assert_eq!(bytes.len(), 32);
+ let mut b2 = [0u8; 32];
+ b2.copy_from_slice(&bytes);
+ c2_Scalar::from_bytes_mod_order(b2)
}
- pub fn finish(self, msg2: &[u8]) -> Result<Vec<u8>, SPAKEErr> {
- if msg2.len() != 1 + G::element_length() {
- return Err(SPAKEErr {
- kind: ErrorType::WrongLength,
- });
- }
- let msg_side = msg2[0];
+ #[test]
+ fn test_convert() {
+ let t1_decimal =
+ b"2238329342913194256032495932344128051776374960164957527413114840482143558222";
+ let t1_scalar = decimal_to_scalar(t1_decimal);
+ let t1_bytes = t1_scalar.to_bytes();
+ let expected = [
+ 0x4e, 0x5a, 0xb4, 0x34, 0x5d, 0x47, 0x08, 0x84, 0x59, 0x13, 0xb4, 0x64, 0x1b, 0xc2,
+ 0x7d, 0x52, 0x52, 0xa5, 0x85, 0x10, 0x1b, 0xcc, 0x42, 0x44, 0xd4, 0x49, 0xf4, 0xa8,
+ 0x79, 0xd9, 0xf2, 0x04,
+ ];
+ assert_eq!(t1_bytes, expected);
+ //println!("t1_scalar is {:?}", t1_scalar);
+ }
- match self.side {
- Side::A => match msg_side {
- 0x42 => (), // 'B'
- _ => {
- return Err(SPAKEErr {
- kind: ErrorType::BadSide,
- })
- }
- },
- Side::B => match msg_side {
- 0x41 => (), // 'A'
- _ => {
- return Err(SPAKEErr {
- kind: ErrorType::BadSide,
- })
- }
- },
- Side::Symmetric => match msg_side {
- 0x53 => (), // 'S'
- _ => {
- return Err(SPAKEErr {
- kind: ErrorType::BadSide,
- })
- }
- },
- }
+ #[test]
+ fn test_serialize_basepoint() {
+ // make sure elements are serialized same as the python library
+ let exp = "5866666666666666666666666666666666666666666666666666666666666666";
+ let base_vec = ED25519_BASEPOINT_POINT.compress().as_bytes().to_vec();
+ let base_hex = hex::encode(base_vec);
+ println!("exp: {:?}", exp);
+ println!("got: {:?}", base_hex);
+ assert_eq!(exp, base_hex);
+ }
- let msg2_element = match G::bytes_to_element(&msg2[1..]) {
- Some(x) => x,
- None => {
- return Err(SPAKEErr {
- kind: ErrorType::CorruptMessage,
- })
- }
- };
+ #[test]
+ fn test_password_to_scalar() {
+ let password = Password::new(b"password");
+ let expected_pw_scalar = decimal_to_scalar(
+ b"3515301705789368674385125653994241092664323519848410154015274772661223168839",
+ );
+ let pw_scalar = Ed25519Group::hash_to_scalar(&password);
+ println!("exp: {:?}", hex::encode(expected_pw_scalar.as_bytes()));
+ println!("got: {:?}", hex::encode(pw_scalar.as_bytes()));
+ assert_eq!(&pw_scalar, &expected_pw_scalar);
+ }
- // a: K = (Y+N*(-pw))*x
- // b: K = (X+M*(-pw))*y
- let unblinding = match self.side {
- Side::A => G::const_n(),
- Side::B => G::const_m(),
- Side::Symmetric => G::const_s(),
- };
- let tmp1 = G::scalarmult(&unblinding, &G::scalar_neg(&self.password_scalar));
- let tmp2 = G::add(&msg2_element, &tmp1);
- let key_element = G::scalarmult(&tmp2, &self.xy_scalar);
- let key_bytes = G::element_to_bytes(&key_element);
+ #[test]
+ fn test_sizes() {
+ let (s1, msg1) = Spake2::<Ed25519Group>::start_a(
+ &Password::new(b"password"),
+ &Identity::new(b"idA"),
+ &Identity::new(b"idB"),
+ );
+ assert_eq!(msg1.len(), 1 + 32);
+ let (s2, msg2) = Spake2::<Ed25519Group>::start_b(
+ &Password::new(b"password"),
+ &Identity::new(b"idA"),
+ &Identity::new(b"idB"),
+ );
+ assert_eq!(msg2.len(), 1 + 32);
+ let key1 = s1.finish(&msg2).unwrap();
+ let key2 = s2.finish(&msg1).unwrap();
+ assert_eq!(key1.len(), 32);
+ assert_eq!(key2.len(), 32);
+
+ let (s1, msg1) = Spake2::<Ed25519Group>::start_symmetric(
+ &Password::new(b"password"),
+ &Identity::new(b"idS"),
+ );
+ assert_eq!(msg1.len(), 1 + 32);
+ let (s2, msg2) = Spake2::<Ed25519Group>::start_symmetric(
+ &Password::new(b"password"),
+ &Identity::new(b"idS"),
+ );
+ assert_eq!(msg2.len(), 1 + 32);
+ let key1 = s1.finish(&msg2).unwrap();
+ let key2 = s2.finish(&msg1).unwrap();
+ assert_eq!(key1.len(), 32);
+ assert_eq!(key2.len(), 32);
+ }
- // key = H(H(pw) + H(idA) + H(idB) + X + Y + K)
- //transcript = b"".join([sha256(pw).digest(),
- // sha256(idA).digest(), sha256(idB).digest(),
- // X_msg, Y_msg, K_bytes])
- //key = sha256(transcript).digest()
- // note that both sides must use the same order
+ #[test]
+ fn test_hash_ab() {
+ let key = ed25519::hash_ab(
+ b"pw",
+ b"idA",
+ b"idB",
+ b"XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX", // len=32
+ b"YYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYY",
+ b"KKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKK",
+ );
+ let expected_key = "d59d9ba920f7092565cec747b08d5b2e981d553ac32fde0f25e5b4a4cfca3efd";
+ assert_eq!(hex::encode(key), expected_key);
+ }
- Ok(match self.side {
- Side::A => ed25519_hash_ab(
- &self.password_vec,
- &self.id_a,
- &self.id_b,
- self.msg1.as_slice(),
- &msg2[1..],
- &key_bytes,
- ),
- Side::B => ed25519_hash_ab(
- &self.password_vec,
- &self.id_a,
- &self.id_b,
- &msg2[1..],
- self.msg1.as_slice(),
- &key_bytes,
- ),
- Side::Symmetric => ed25519_hash_symmetric(
- &self.password_vec,
- &self.id_s,
- &self.msg1,
- &msg2[1..],
- &key_bytes,
- ),
- })
+ #[test]
+ fn test_hash_symmetric() {
+ let key = ed25519::hash_symmetric(
+ b"pw",
+ b"idSymmetric",
+ b"XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX",
+ b"YYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYY",
+ b"KKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKK",
+ );
+ let expected_key = "b0b31e4401aae37d91a9a8bf6fbb1298cafc005ff9142e3ffc5b9799fb11128b";
+ assert_eq!(hex::encode(key), expected_key);
}
-}
-fn maybe_utf8(s: &[u8]) -> String {
- match String::from_utf8(s.to_vec()) {
- Ok(m) => format!("(s={})", m),
- Err(_) => format!("(hex={})", hex::encode(s)),
+ #[test]
+ fn test_asymmetric() {
+ let scalar_a = decimal_to_scalar(
+ b"2611694063369306139794446498317402240796898290761098242657700742213257926693",
+ );
+ let scalar_b = decimal_to_scalar(
+ b"7002393159576182977806091886122272758628412261510164356026361256515836884383",
+ );
+ let expected_pw_scalar = decimal_to_scalar(
+ b"3515301705789368674385125653994241092664323519848410154015274772661223168839",
+ );
+
+ println!("scalar_a is {}", hex::encode(scalar_a.as_bytes()));
+
+ let (s1, msg1) = Spake2::<Ed25519Group>::start_a_internal(
+ &Password::new(b"password"),
+ &Identity::new(b"idA"),
+ &Identity::new(b"idB"),
+ scalar_a,
+ );
+ let expected_msg1 = "416fc960df73c9cf8ed7198b0c9534e2e96a5984bfc5edc023fd24dacf371f2af9";
+
+ println!();
+ println!("xys1: {:?}", hex::encode(s1.xy_scalar.as_bytes()));
+ println!();
+ println!("pws1: {:?}", hex::encode(s1.password_scalar.as_bytes()));
+ println!("exp : {:?}", hex::encode(expected_pw_scalar.as_bytes()));
+ println!();
+ println!("msg1: {:?}", hex::encode(&msg1));
+ println!("exp : {:?}", expected_msg1);
+ println!();
+
+ assert_eq!(
+ hex::encode(expected_pw_scalar.as_bytes()),
+ hex::encode(s1.password_scalar.as_bytes())
+ );
+ assert_eq!(hex::encode(&msg1), expected_msg1);
+
+ let (s2, msg2) = Spake2::<Ed25519Group>::start_b_internal(
+ &Password::new(b"password"),
+ &Identity::new(b"idA"),
+ &Identity::new(b"idB"),
+ scalar_b,
+ );
+ assert_eq!(expected_pw_scalar, s2.password_scalar);
+ assert_eq!(
+ hex::encode(&msg2),
+ "42354e97b88406922b1df4bea1d7870f17aed3dba7c720b313edae315b00959309"
+ );
+
+ let key1 = s1.finish(&msg2).unwrap();
+ let key2 = s2.finish(&msg1).unwrap();
+ assert_eq!(key1, key2);
+ assert_eq!(
+ hex::encode(key1),
+ "712295de7219c675ddd31942184aa26e0a957cf216bc230d165b215047b520c1"
+ );
}
-}
-impl<G: Group> fmt::Debug for SPAKE2<G> {
- fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
- fmt.debug_struct("SPAKE2")
- .field("group", &G::name())
- .field("side", &self.side)
- .field("idA", &maybe_utf8(&self.id_a))
- .field("idB", &maybe_utf8(&self.id_b))
- .field("idS", &maybe_utf8(&self.id_s))
- .finish()
+ #[test]
+ fn test_debug() {
+ let (s1, _msg1) = Spake2::<Ed25519Group>::start_a(
+ &Password::new(b"password"),
+ &Identity::new(b"idA"),
+ &Identity::new(b"idB"),
+ );
+ println!("s1: {:?}", s1);
+ assert_eq!(
+ format!("{:?}", s1),
+ "SPAKE2 { group: \"Ed25519\", side: A, idA: (s=idA), idB: (s=idB), idS: (s=) }"
+ );
+
+ let (s2, _msg1) = Spake2::<Ed25519Group>::start_symmetric(
+ &Password::new(b"password"),
+ &Identity::new(b"idS"),
+ );
+ println!("s2: {:?}", s2);
+ assert_eq!(
+ format!("{:?}", s2),
+ "SPAKE2 { group: \"Ed25519\", side: Symmetric, idA: (s=), idB: (s=), idS: (s=idS) }"
+ );
}
}
-
-#[cfg(test)]
-mod tests;
projects / PAKEs.git / blobdiff