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srp: add no_username_in_x option #220

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Merged
tarcieri merged 2 commits into from
Dec 24, 2025
Merged

srp: add no_username_in_x option #220

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b2bcd77
Bring back the no_username_in_x option from PR RustCrypto/PAKEs#153
Dadoum Dec 24, 2025
a6f1d77
fix: rustfmt
Dadoum Dec 24, 2025
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20 changes: 17 additions & 3 deletions srp/src/client.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -114,6 +114,7 @@ use crate::utils::{
/// SRP client state before handshake with the server.
pub struct SrpClient<'a, D: Digest> {
params: &'a SrpGroup,
no_user_in_x: bool,
d: PhantomData<D>,
}

Expand All @@ -138,6 +139,16 @@ impl<'a, D: Digest> SrpClient<'a, D> {
pub const fn new(params: &'a SrpGroup) -> Self {
Self {
params,
no_user_in_x: false,
d: PhantomData,
}
}

#[must_use]
pub const fn new_with_options(params: &'a SrpGroup, no_user_in_x: bool) -> Self {
Self {
params,
no_user_in_x,
d: PhantomData,
}
}
Expand Down Expand Up @@ -197,7 +208,8 @@ impl<'a, D: Digest> SrpClient<'a, D> {
/// Get password verifier (v in RFC5054) for user registration on the server.
#[must_use]
pub fn compute_verifier(&self, username: &[u8], password: &[u8], salt: &[u8]) -> Vec<u8> {
let identity_hash = Self::compute_identity_hash(username, password);
let identity_username = if self.no_user_in_x { &[] } else { username };
let identity_hash = Self::compute_identity_hash(identity_username, password);
let x = Self::compute_x(identity_hash.as_slice(), salt);
self.compute_v(&x).to_bytes_be()
}
Expand Down Expand Up @@ -232,7 +244,8 @@ impl<'a, D: Digest> SrpClient<'a, D> {

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 identity_username = if self.no_user_in_x { &[] } else { username };
let identity_hash = Self::compute_identity_hash(identity_username, password);
let x = Self::compute_x(identity_hash.as_slice(), salt);

let key = self.compute_premaster_secret(&b_pub, &k, &x, &a, &u);
Expand Down Expand Up @@ -275,7 +288,8 @@ impl<'a, D: Digest> SrpClient<'a, D> {

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 identity_username = if self.no_user_in_x { &[] } else { username };
let identity_hash = Self::compute_identity_hash(identity_username, password);
let x = Self::compute_x(identity_hash.as_slice(), salt);

let premaster_secret = self
Expand Down