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authorАртём Павлов [Artyom Pavlov] <newpavlov@gmail.com>2017-08-14 07:37:17 +0300
committerАртём Павлов [Artyom Pavlov] <newpavlov@gmail.com>2017-08-14 07:37:17 +0300
commit331727194c231a10dc2e296922e09aa0e888f4bd (patch)
tree46e2a32679f399a7584b3b33d3986611195a395c /src/client.rs
parentdefd41c0ee00cf06930b733e9ab06163bc6ad1cf (diff)
downloadPAKEs-331727194c231a10dc2e296922e09aa0e888f4bd.tar.xz
PAKE repository reorganization
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-//! SRP client implementation.
-//!
-//! # Usage
-//! First create SRP client struct by passing to it SRP parameters (shared
-//! between client and server) and randomly generated `a`:
-//!
-//! ```ignore
-//! use srp::groups::G_2048;
-//! use sha2::Sha256;
-//!
-//! let a = rng.gen_iter::<u8>().take(64).collect::<Vec<u8>>();
-//! let client = SrpClient::<Sha256>::new(&a, &G_2048);
-//! ```
-//!
-//! Next send handshake data (username and `a_pub`) to the server and receive
-//! `salt` and `b_pub`:
-//!
-//! ```ignore
-//! let a_pub = client.get_a_pub();
-//! let (salt, b_pub) = conn.send_handshake(username, a_pub);
-//! ```
-//!
-//! Compute private key using `salt` with any password hashing function.
-//! You can use method from SRP-6a, but it's recommended to use specialized
-//! password hashing algorithm instead (e.g. PBKDF2, argon2 or scrypt).
-//! Next create verifier instance, note that `get_verifier` consumes client and
-//! can return error in case of malicious `b_pub`.
-//!
-//! ```ignore
-//! let private_key = srp_private_key::<Sha256>(username, password, salt);
-//! let verifier = client.get_verifier(&private_key, &b_pub)?;
-//! ```
-//!
-//! Finally verify the server: first generate user proof,
-//! send it to the server and verify server proof in the reply. Note that
-//! `verify_server` method will return error in case of incorrect server reply.
-//!
-//! ```ignore
-//! let user_proof = verifier.get_proof();
-//! let server_proof = conn.send_proof(user_proof);
-//! let key = verifier.verify_server(server_proof)?;
-//! ```
-//!
-//! `key` contains shared secret key between user and the server. Alternatively
-//! you can directly extract shared secret key using `get_key()` method and
-//! handle authentification through different (secure!) means (e.g. by using
-//! authentificated cipher mode).
-//!
-//! For user registration on the server first generate salt (e.g. 32 bytes long)
-//! and get password verifier which depends on private key. Send useranme, salt
-//! and password verifier over protected channel to protect against MitM for
-//! registration.
-//!
-//! ```ignore
-//! let pwd_verifier = client.get_password_verifier(&private_key);
-//! conn.send_registration_data(username, salt, pwd_verifier);
-//! ```
-
-//let buf = rng.gen_iter::<u8>().take(l).collect::<Vec<u8>>();
-use std::marker::PhantomData;
-
-use num::{BigUint, Zero};
-use digest::Digest;
-use generic_array::GenericArray;
-
-use tools::powm;
-use types::{SrpAuthError, SrpGroup};
-
-/// SRP client state before handshake with the server.
-pub struct SrpClient<'a, D: Digest> {
- params: &'a SrpGroup,
-
- a: BigUint,
- a_pub: BigUint,
-
- d: PhantomData<D>
-}
-
-/// SRP client state after handshake with the server.
-pub struct SrpClientVerifier<D: Digest> {
- proof: GenericArray<u8, D::OutputSize>,
- server_proof: GenericArray<u8, D::OutputSize>,
- key: GenericArray<u8, D::OutputSize>,
-}
-
-/// Compute user private key as described in the RFC 5054. Consider using proper
-/// password hashing algorithm instead.
-pub fn srp_private_key<D: Digest>(username: &[u8], password: &[u8], salt: &[u8])
- -> GenericArray<u8, D::OutputSize>
-{
- let p = {
- let mut d = D::new();
- d.input(username);
- d.input(b":");
- d.input(password);
- d.result()
- };
- let mut d = D::new();
- d.input(salt);
- d.input(&p);
- d.result()
-}
-
-impl<'a, D: Digest> SrpClient<'a, D> {
- /// Create new SRP client instance.
- pub fn new(a: &[u8], params: &'a SrpGroup) -> Self {
- let a = BigUint::from_bytes_be(a);
- let a_pub = params.powm(&a);
-
- Self { params, a, a_pub, d: Default::default() }
- }
-
- /// Get password verfier for user registration on the server
- pub fn get_password_verifier(&self, private_key: &[u8]) -> Vec<u8> {
- let x = BigUint::from_bytes_be(&private_key);
- let v = self.params.powm(&x);
- v.to_bytes_be()
- }
-
- fn calc_key(&self, b_pub: &BigUint, x: &BigUint, u: &BigUint)
- -> GenericArray<u8, D::OutputSize>
- {
- let n = &self.params.n;
- let k = self.params.compute_k::<D>();
- let interm = (k * self.params.powm(x)) % n;
- // Because we do operation in modulo N we can get: (kv + g^b) < kv
- let v = if b_pub > &interm {
- (b_pub - &interm) % n
- } else {
- (n + b_pub - &interm) % n
- };
- // S = |B - kg^x| ^ (a + ux)
- let s = powm(&v, &(&self.a + (u*x) % n ), n);
- D::digest(&s.to_bytes_be())
- }
-
- /// Process server reply to the handshake.
- pub fn process_reply(self, private_key: &[u8], b_pub: &[u8])
- -> Result<SrpClientVerifier<D>, SrpAuthError>
- {
- let u = {
- let mut d = D::new();
- d.input(&self.a_pub.to_bytes_be());
- d.input(b_pub);
- BigUint::from_bytes_be(&d.result())
- };
-
- let b_pub = BigUint::from_bytes_be(b_pub);
-
- // Safeguard against malicious B
- if &b_pub % &self.params.n == BigUint::zero() {
- return Err(SrpAuthError{ description: "Malicious b_pub value" })
- }
-
- let x = BigUint::from_bytes_be(&private_key);
- let key = self.calc_key(&b_pub, &x, &u);
- // M1 = H(A, B, K)
- let proof = {
- let mut d = D::new();
- d.input(&self.a_pub.to_bytes_be());
- d.input(&b_pub.to_bytes_be());
- d.input(&key);
- d.result()
- };
-
- // M2 = H(A, M1, K)
- let server_proof = {
- let mut d = D::new();
- d.input(&self.a_pub.to_bytes_be());
- d.input(&proof);
- d.input(&key);
- d.result()
- };
-
- Ok(SrpClientVerifier {
- proof: proof,
- server_proof: server_proof,
- key: key,
- })
- }
-
- /// Get public ephemeral value for handshaking with the server.
- pub fn get_a_pub(&self) -> Vec<u8> {
- self.a_pub.to_bytes_be()
- }
-}
-
-impl<D: Digest> SrpClientVerifier<D> {
- /// Get shared secret key without authenticating server, e.g. for using with
- /// authenticated encryption modes. DO NOT USE this method without
- /// some kind of secure authentification.
- pub fn get_key(self) -> GenericArray<u8, D::OutputSize> {
- self.key
- }
-
- /// Verification data for sending to the server.
- pub fn get_proof(&self) -> GenericArray<u8, D::OutputSize> {
- self.proof.clone()
- }
-
- /// Verify server reply to verification data. It will return shared secret
- /// key in case of success.
- pub fn verify_server(self, reply: &[u8])
- -> Result<GenericArray<u8, D::OutputSize>, SrpAuthError>
- {
- if self.server_proof.as_slice() != reply {
- Err(SrpAuthError{ description: "Incorrect server proof" })
- } else {
- Ok(self.key)
- }
- }
-}