From 306e40b7967ad11670cc1c9403b5a88073fecc4b Mon Sep 17 00:00:00 2001
From: Tony Arcieri <bascule@gmail.com>
Date: Sun, 18 Oct 2026 15:02:38 -0700
Subject: [PATCH] Use `os2ip` for decoding signatures

Uses the helper function introduced in #719 for signature decoding
---
 src/pkcs1v15.rs |  7 +++----
 src/pss.rs      | 13 +++++--------
 2 files changed, 8 insertions(+), 12 deletions(-)

diff --git a/src/pkcs1v15.rs b/src/pkcs1v15.rs
index 6b2178e2..85f95621 100644
--- a/src/pkcs1v15.rs
+++ b/src/pkcs1v15.rs
@@ -42,7 +42,6 @@ pub use self::{
 use alloc::{boxed::Box, vec::Vec};
 use const_oid::AssociatedOid;
 use core::fmt::Debug;
-use crypto_bigint::BoxedUint;
 use digest::Digest;
 use rand_core::TryCryptoRng;
 
@@ -207,7 +206,7 @@ fn sign<R: TryCryptoRng + ?Sized>(
 ) -> Result<Vec<u8>> {
     let em = pkcs1v15_sign_pad(prefix, hashed, priv_key.size())?;
 
-    let em = BoxedUint::from_be_slice(&em, priv_key.n_bits_precision())?;
+    let em = os2ip(&em, priv_key.n_bits_precision())?;
     // The signature itself is public; only the computation is secret
     Ok(i2osp(
         rsa_decrypt_and_check(priv_key, rng, &em)?,
@@ -222,8 +221,7 @@ fn verify(pub_key: &RsaPublicKey, prefix: &[u8], hashed: &[u8], sig: &[u8]) -> R
     if sig.len() != pub_key.size() {
         return Err(Error::Verification);
     }
-    let s = BoxedUint::from_be_slice(sig, pub_key.n_bits_precision())
-        .map_err(|_| Error::Verification)?;
+    let s = os2ip(sig, pub_key.n_bits_precision()).map_err(|_| Error::Verification)?;
     if s >= *pub_key.n().as_ref() {
         return Err(Error::Verification);
     }
@@ -284,6 +282,7 @@ mod tests {
         SignatureEncoding, Signer, Verifier,
     };
     use base64ct::{Base64, Encoding};
+    use crypto_bigint::BoxedUint;
     use hex_literal::hex;
     use rand::rngs::ChaCha8Rng;
     use rand_core::{Rng, SeedableRng};
diff --git a/src/pss.rs b/src/pss.rs
index e4ed2c1f..4841ffe7 100644
--- a/src/pss.rs
+++ b/src/pss.rs
@@ -21,12 +21,11 @@ pub use self::{
 
 use alloc::vec::Vec;
 use core::fmt::{self, Debug};
-use crypto_bigint::BoxedUint;
 
 use digest::{Digest, FixedOutputReset};
 use rand_core::TryCryptoRng;
 
-use crate::algorithms::pad::i2osp;
+use crate::algorithms::pad::{i2osp, os2ip};
 use crate::algorithms::pss::*;
 use crate::algorithms::rsa::{rsa_decrypt_and_check, rsa_encrypt};
 use crate::errors::{Error, Result};
@@ -148,8 +147,7 @@ where
     if sig.len() != pub_key.size() {
         return Err(Error::Verification);
     }
-    let s = BoxedUint::from_be_slice(sig, pub_key.n_bits_precision())
-        .map_err(|_| Error::Verification)?;
+    let s = os2ip(sig, pub_key.n_bits_precision()).map_err(|_| Error::Verification)?;
     let raw = rsa_encrypt(pub_key, &s)?;
     let mut em = i2osp(raw, pub_key.size());
 
@@ -168,8 +166,7 @@ where
     if sig.len() != pub_key.size() {
         return Err(Error::Verification);
     }
-    let s = BoxedUint::from_be_slice(sig, pub_key.n_bits_precision())
-        .map_err(|_| Error::Verification)?;
+    let s = os2ip(sig, pub_key.n_bits_precision()).map_err(|_| Error::Verification)?;
     if s >= *pub_key.n().as_ref() {
         return Err(Error::Verification);
     }
@@ -239,7 +236,7 @@ where
 
     let em = emsa_pss_encode(hashed, em_bits as _, salt, digest)?;
 
-    let em = BoxedUint::from_be_slice(&em, priv_key.n_bits_precision())?;
+    let em = os2ip(&em, priv_key.n_bits_precision())?;
     let raw = rsa_decrypt_and_check(priv_key, blind_rng, &em)?;
     Ok(i2osp(raw, priv_key.size()))
 }
@@ -257,7 +254,7 @@ where
     let em_bits = priv_key.n().bits() - 1;
     let em = emsa_pss_encode_digest::<D>(hashed, em_bits as _, salt)?;
 
-    let em = BoxedUint::from_be_slice(&em, priv_key.n_bits_precision())?;
+    let em = os2ip(&em, priv_key.n_bits_precision())?;
     Ok(i2osp(
         rsa_decrypt_and_check(priv_key, blind_rng, &em)?,
         priv_key.size(),