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Standard implementation option #153

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Standard implementation option #153

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f01e9b9
Implemented standard implementation option and also added an option t…
masihyeganeh Sep 15, 2023
f4ffa0f
Make clippy happy
masihyeganeh Sep 15, 2023
15cb641
Alternate implementation
masihyeganeh Sep 21, 2023
6cd45bb
Fix documentation and unify some names
masihyeganeh Sep 21, 2023
8c163b4
Fix documentation tests
masihyeganeh Sep 21, 2023
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105 changes: 103 additions & 2 deletions srp/src/client.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -64,7 +64,23 @@
//! # let verifier = client.process_reply(b"", b"", b"", b"", b"1").unwrap();
//!
//! verifier.key();
//!```
//! ```
//!
//!
//! Alternatively, you can use `process_reply_rfc5054` method to process parameters
//! according to RFC 5054 if the server is using it. This way, it generates M1 and
//! M2 differently and also the `verify_server` method will return a shared session
//! key in case of correct server data.
//!
//! ```rust
//! # let client = crate::srp::client::SrpClient::<sha2::Sha256>::new(&crate::srp::groups::G_2048);
//! # let verifier = client.process_reply_rfc5054(b"", b"", b"", b"", b"1").unwrap();
//! # fn send_proof(_: &[u8]) -> Vec<u8> { vec![10, 215, 214, 40, 136, 200, 122, 121, 68, 160, 38, 32, 85, 82, 128, 30, 199, 194, 126, 222, 61, 55, 2, 28, 120, 181, 155, 102, 141, 65, 17, 64] }
//!
//! let client_proof = verifier.proof();
//! let server_proof = send_proof(client_proof);
//! let session_key = verifier.verify_server(&server_proof).unwrap();
//! ```
//!
//!
//! For user registration on the server first generate salt (e.g. 32 bytes long)
Expand All @@ -82,6 +98,7 @@
//! let pwd_verifier = client.compute_verifier(username, password, salt);
//! send_registration_data(username, salt, &pwd_verifier);
//! ```
//!

use std::marker::PhantomData;

Expand All @@ -90,7 +107,9 @@ use num_bigint::BigUint;
use subtle::ConstantTimeEq;

use crate::types::{SrpAuthError, SrpGroup};
use crate::utils::{compute_k, compute_m1, compute_m2, compute_u};
use crate::utils::{
compute_hash, compute_k, compute_m1, compute_m1_rfc5054, compute_m2, compute_u,
};

/// SRP client state before handshake with the server.
pub struct SrpClient<'a, D: Digest> {
Expand All @@ -105,6 +124,14 @@ pub struct SrpClientVerifier<D: Digest> {
key: Vec<u8>,
}

/// RFC 5054 SRP client state after handshake with the server.
pub struct SrpClientVerifierRfc5054<D: Digest> {
m1: Output<D>,
m2: Output<D>,
key: Vec<u8>,
session_key: Vec<u8>,
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I think you can use D::Output for session_key.

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Yes, I think we can use D::Output as long as we have a getter method that returns this in a more primitive type, because at least in my use-case, this session key is used for every encryption after the key agreement.
It is nicer to hide away all these types used internally before the output

}

impl<'a, D: Digest> SrpClient<'a, D> {
/// Create new SRP client instance.
#[must_use]
Expand Down Expand Up @@ -224,6 +251,57 @@ impl<'a, D: Digest> SrpClient<'a, D> {
key: key.to_bytes_be(),
})
}

/// Process server reply to the handshake according to RFC 5054.
/// `a` is a random value,
/// `username`, `password` is supplied by the user
/// `salt` and `b_pub` come from the server
pub fn process_reply_rfc5054(
&self,
a: &[u8],
username: &[u8],
password: &[u8],
salt: &[u8],
b_pub: &[u8],
) -> Result<SrpClientVerifierRfc5054<D>, SrpAuthError> {
let a = BigUint::from_bytes_be(a);
let a_pub = self.compute_a_pub(&a);
let b_pub = BigUint::from_bytes_be(b_pub);

// Safeguard against malicious B
if &b_pub % &self.params.n == BigUint::default() {
return Err(SrpAuthError::IllegalParameter("b_pub".to_owned()));
}

let u = compute_u::<D>(&a_pub.to_bytes_be(), &b_pub.to_bytes_be());
let k = compute_k::<D>(self.params);
let identity_hash = Self::compute_identity_hash(username, password);
let x = Self::compute_x(identity_hash.as_slice(), salt);

let premaster_secret = self
.compute_premaster_secret(&b_pub, &k, &x, &a, &u)
.to_bytes_be();

let session_key = compute_hash::<D>(&premaster_secret);

let m1 = compute_m1_rfc5054::<D>(
self.params,
username,
salt,
&a_pub.to_bytes_be(),
&b_pub.to_bytes_be(),
session_key.as_slice(),
);

let m2 = compute_m2::<D>(&a_pub.to_bytes_be(), &m1, session_key.as_slice());

Ok(SrpClientVerifierRfc5054 {
m1,
m2,
key: premaster_secret,
session_key: session_key.to_vec(),
})
}
}

impl<D: Digest> SrpClientVerifier<D> {
Expand All @@ -248,3 +326,26 @@ impl<D: Digest> SrpClientVerifier<D> {
}
}
}

impl<D: Digest> SrpClientVerifierRfc5054<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 authentication
pub fn key(&self) -> &[u8] {
&self.key
}

/// Verification data for sending to the server.
pub fn proof(&self) -> &[u8] {
self.m1.as_slice()
}

/// Verify server reply to verification data and return shared session key.
pub fn verify_server(&self, reply: &[u8]) -> Result<&[u8], SrpAuthError> {
if self.m2.ct_eq(reply).unwrap_u8() == 1 {
Ok(self.session_key.as_slice())
} else {
Err(SrpAuthError::BadRecordMac("server".to_owned()))
}
}
}
105 changes: 103 additions & 2 deletions srp/src/server.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -57,7 +57,25 @@
//! # let verifier = server.process_reply(b"", b"", b"1").unwrap();
//!
//! verifier.key();
//!```
//! ```
//!
//!
//! Alternatively, you can use `process_reply_rfc5054` method to process parameters
//! according to RFC 5054 if the client is using it. You need to pass `username` and
//! `salt` in addition to other parameters to this method. This way, it generates M1
//! and M2 differently and also the `verify_client` method will return a shared session
//! key in case of correct server data.
//!
//! ```rust
//! # let server = crate::srp::server::SrpServer::<sha2::Sha256>::new(&crate::srp::groups::G_2048);
//! # let verifier = server.process_reply_rfc5054(b"", b"", b"", b"", b"1").unwrap();
//! # fn get_client_proof()-> Vec<u8> { vec![53, 91, 252, 129, 223, 201, 97, 145, 208, 243, 229, 232, 20, 118, 108, 126, 244, 68, 237, 38, 121, 24, 181, 53, 155, 103, 134, 44, 107, 204, 56, 50] };
//! # fn send_proof(_: &[u8]) { };
//!
//! let client_proof = get_client_proof();
//! let session_key = verifier.verify_client(&client_proof).unwrap();
//! send_proof(verifier.proof());
//! ```
//!
use std::marker::PhantomData;

Expand All @@ -66,7 +84,9 @@ use num_bigint::BigUint;
use subtle::ConstantTimeEq;

use crate::types::{SrpAuthError, SrpGroup};
use crate::utils::{compute_k, compute_m1, compute_m2, compute_u};
use crate::utils::{
compute_hash, compute_k, compute_m1, compute_m1_rfc5054, compute_m2, compute_u,
};

/// SRP server state
pub struct SrpServer<'a, D: Digest> {
Expand All @@ -81,6 +101,14 @@ pub struct SrpServerVerifier<D: Digest> {
key: Vec<u8>,
}

/// RFC 5054 SRP server state after handshake with the client.
pub struct SrpServerVerifierRfc5054<D: Digest> {
m1: Output<D>,
m2: Output<D>,
key: Vec<u8>,
session_key: Vec<u8>,
}

impl<'a, D: Digest> SrpServer<'a, D> {
/// Create new server state.
#[must_use]
Expand Down Expand Up @@ -162,6 +190,56 @@ impl<'a, D: Digest> SrpServer<'a, D> {
key: key.to_bytes_be(),
})
}

/// Process client reply to the handshake according to RFC 5054.
/// b is a random value,
/// v is the provided during initial user registration
pub fn process_reply_rfc5054(
&self,
username: &[u8],
salt: &[u8],
b: &[u8],
v: &[u8],
a_pub: &[u8],
) -> Result<SrpServerVerifierRfc5054<D>, SrpAuthError> {
let b = BigUint::from_bytes_be(b);
let v = BigUint::from_bytes_be(v);
let a_pub = BigUint::from_bytes_be(a_pub);

let k = compute_k::<D>(self.params);
let b_pub = self.compute_b_pub(&b, &k, &v);

// Safeguard against malicious A
if &a_pub % &self.params.n == BigUint::default() {
return Err(SrpAuthError::IllegalParameter("a_pub".to_owned()));
}

let u = compute_u::<D>(&a_pub.to_bytes_be(), &b_pub.to_bytes_be());

let premaster_secret = self
.compute_premaster_secret(&a_pub, &v, &u, &b)
.to_bytes_be();

let session_key = compute_hash::<D>(&premaster_secret);

let m1 = compute_m1_rfc5054::<D>(
self.params,
username,
salt,
&a_pub.to_bytes_be(),
&b_pub.to_bytes_be(),
session_key.as_slice(),
);

let m2 = compute_m2::<D>(&a_pub.to_bytes_be(), &m1, session_key.as_slice());

Ok(SrpServerVerifierRfc5054 {
m1,
m2,
key: premaster_secret,
session_key: session_key.to_vec(),
})
}
}

impl<D: Digest> SrpServerVerifier<D> {
Expand All @@ -186,3 +264,26 @@ impl<D: Digest> SrpServerVerifier<D> {
}
}
}

impl<D: Digest> SrpServerVerifierRfc5054<D> {
/// Get shared secret between user and the server. (do not forget to verify
/// that keys are the same!)
pub fn key(&self) -> &[u8] {
&self.key
}

/// Verification data for sending to the client.
pub fn proof(&self) -> &[u8] {
// TODO not Output
self.m2.as_slice()
}

/// Process user proof of having the same shared secret and return shared session key.
pub fn verify_client(&self, reply: &[u8]) -> Result<&[u8], SrpAuthError> {
if self.m1.ct_eq(reply).unwrap_u8() == 1 {
Ok(self.session_key.as_slice())
} else {
Err(SrpAuthError::BadRecordMac("client".to_owned()))
}
}
}
46 changes: 45 additions & 1 deletion srp/src/utils.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -27,8 +27,25 @@ pub fn compute_k<D: Digest>(params: &SrpGroup) -> BigUint {
BigUint::from_bytes_be(d.finalize().as_slice())
}

// H(N) XOR H(PAD(g))
#[must_use]
pub fn compute_hash_n_xor_hash_g<D: Digest>(params: &SrpGroup) -> Vec<u8> {
let n = params.n.to_bytes_be();
let g_bytes = params.g.to_bytes_be();
let mut buf = vec![0u8; n.len()];
let l = n.len() - g_bytes.len();
buf[l..].copy_from_slice(&g_bytes);

let h_n = compute_hash::<D>(&n).to_vec();
let h_g = compute_hash::<D>(&buf).to_vec();

h_n.iter()
.zip(h_g.iter())
.map(|(&x1, &x2)| x1 ^ x2)
.collect()
}

// M1 = H(A, B, K) this doesn't follow the spec but apparently no one does for M1
// M1 should equal = H(H(N) XOR H(g) | H(U) | s | A | B | K) according to the spec
#[must_use]
pub fn compute_m1<D: Digest>(a_pub: &[u8], b_pub: &[u8], key: &[u8]) -> Output<D> {
let mut d = D::new();
Expand All @@ -38,6 +55,33 @@ pub fn compute_m1<D: Digest>(a_pub: &[u8], b_pub: &[u8], key: &[u8]) -> Output<D
d.finalize()
}

#[must_use]
pub fn compute_hash<D: Digest>(data: &[u8]) -> Output<D> {
let mut d = D::new();
d.update(data);
d.finalize()
}

// M1 = H(H(N) XOR H(g) | H(U) | s | A | B | K) following RFC5054
#[must_use]
pub fn compute_m1_rfc5054<D: Digest>(
params: &SrpGroup,
username: &[u8],
salt: &[u8],
a_pub: &[u8],
b_pub: &[u8],
key: &[u8],
) -> Output<D> {
let mut d = D::new();
d.update(compute_hash_n_xor_hash_g::<D>(params));
d.update(compute_hash::<D>(username));
d.update(salt);
d.update(a_pub);
d.update(b_pub);
d.update(key);
d.finalize()
}

// M2 = H(A, M1, K)
#[must_use]
pub fn compute_m2<D: Digest>(a_pub: &[u8], m1: &Output<D>, key: &[u8]) -> Output<D> {
Expand Down
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