pss, oaep: remove DynDigest

I'm not sure I see why usage of `DynDigest` was originally introduced.
The need to make the Digest also Send is hard to use in downstream
crates.
I don't believe this was necessary, this removes its use and makes the
consumer specify the Digest types.

Author: baloo

src/algorithms/mgf.rs

@@ -1,11 +1,14 @@
 //! Mask generation function common to both PSS and OAEP padding
 
-use digest::{Digest, DynDigest, FixedOutputReset};
+use digest::{Digest, FixedOutputReset};
 
 /// Mask generation function.
 ///
 /// Panics if out is larger than 2**32. This is in accordance with RFC 8017 - PKCS #1 B.2.1
-pub(crate) fn mgf1_xor(out: &mut [u8], digest: &mut dyn DynDigest, seed: &[u8]) {
+pub(crate) fn mgf1_xor<D>(out: &mut [u8], digest: &mut D, seed: &[u8])
+where
+    D: Digest + FixedOutputReset,
+{
     let mut counter = [0u8; 4];
     let mut i = 0;
 
@@ -17,7 +20,7 @@ pub(crate) fn mgf1_xor(out: &mut [u8], digest: &mut dyn DynDigest, seed: &[u8])
         digest_input[0..seed.len()].copy_from_slice(seed);
         digest_input[seed.len()..].copy_from_slice(&counter);
 
-        digest.update(digest_input.as_slice());
+        Digest::update(digest, digest_input.as_slice());
         let digest_output = &*digest.finalize_reset();
         let mut j = 0;
         loop {

src/algorithms/oaep.rs

@@ -3,7 +3,7 @@
 use alloc::boxed::Box;
 use alloc::vec::Vec;
 
-use digest::{Digest, DynDigest, FixedOutputReset};
+use digest::{Digest, FixedOutputReset};
 use rand_core::TryCryptoRng;
 use subtle::{Choice, ConditionallySelectable, ConstantTimeEq, CtOption};
 use zeroize::Zeroizing;
@@ -57,22 +57,27 @@ fn encrypt_internal<R: TryCryptoRng + ?Sized, MGF: FnMut(&mut [u8], &mut [u8])>(
 ///
 /// [PKCS#1 OAEP]: https://datatracker.ietf.org/doc/html/rfc8017#section-7.1
 #[inline]
-pub(crate) fn oaep_encrypt<R: TryCryptoRng + ?Sized>(
+pub(crate) fn oaep_encrypt<R, D, MGD>(
     rng: &mut R,
     msg: &[u8],
-    digest: &mut dyn DynDigest,
-    mgf_digest: &mut dyn DynDigest,
+    digest: &mut D,
+    mgf_digest: &mut MGD,
     label: Option<Box<[u8]>>,
     k: usize,
-) -> Result<Zeroizing<Vec<u8>>> {
-    let h_size = digest.output_size();
+) -> Result<Zeroizing<Vec<u8>>>
+where
+    R: TryCryptoRng + ?Sized,
+    D: Digest + FixedOutputReset,
+    MGD: Digest + FixedOutputReset,
+{
+    let h_size = <D as Digest>::output_size();
 
     let label = label.unwrap_or_default();
     if label.len() as u64 >= MAX_LABEL_LEN {
         return Err(Error::LabelTooLong);
     }
 
-    digest.update(&label);
+    Digest::update(digest, &label);
     let p_hash = digest.finalize_reset();
 
     encrypt_internal(rng, msg, &p_hash, h_size, k, |seed, db| {
@@ -89,16 +94,17 @@ pub(crate) fn oaep_encrypt<R: TryCryptoRng + ?Sized>(
 ///
 /// [PKCS#1 OAEP]: https://datatracker.ietf.org/doc/html/rfc8017#section-7.1
 #[inline]
-pub(crate) fn oaep_encrypt_digest<
-    R: TryCryptoRng + ?Sized,
-    D: Digest,
-    MGD: Digest + FixedOutputReset,
->(
+pub(crate) fn oaep_encrypt_digest<R, D, MGD>(
     rng: &mut R,
     msg: &[u8],
     label: Option<Box<[u8]>>,
     k: usize,
-) -> Result<Zeroizing<Vec<u8>>> {
+) -> Result<Zeroizing<Vec<u8>>>
+where
+    R: TryCryptoRng + ?Sized,
+    D: Digest,
+    MGD: Digest + FixedOutputReset,
+{
     let h_size = <D as Digest>::output_size();
 
     let label = label.unwrap_or_default();
@@ -126,21 +132,25 @@ pub(crate) fn oaep_encrypt_digest<
 ///
 /// [PKCS#1 OAEP]: https://datatracker.ietf.org/doc/html/rfc8017#section-7.1
 #[inline]
-pub(crate) fn oaep_decrypt(
+pub(crate) fn oaep_decrypt<D, MGD>(
     em: &mut [u8],
-    digest: &mut dyn DynDigest,
-    mgf_digest: &mut dyn DynDigest,
+    digest: &mut D,
+    mgf_digest: &mut MGD,
     label: Option<Box<[u8]>>,
     k: usize,
-) -> Result<Vec<u8>> {
-    let h_size = digest.output_size();
+) -> Result<Vec<u8>>
+where
+    D: Digest + FixedOutputReset,
+    MGD: Digest + FixedOutputReset,
+{
+    let h_size = <D as Digest>::output_size();
 
     let label = label.unwrap_or_default();
     if label.len() as u64 >= MAX_LABEL_LEN {
         return Err(Error::Decryption);
     }
 
-    digest.update(&label);
+    Digest::update(digest, &label);
 
     let expected_p_hash = digest.finalize_reset();
 
@@ -168,11 +178,15 @@ pub(crate) fn oaep_decrypt(
 ///
 /// [PKCS#1 OAEP]: https://datatracker.ietf.org/doc/html/rfc8017#section-7.1
 #[inline]
-pub(crate) fn oaep_decrypt_digest<D: Digest, MGD: Digest + FixedOutputReset>(
+pub(crate) fn oaep_decrypt_digest<D, MGD>(
     em: &mut [u8],
     label: Option<Box<[u8]>>,
     k: usize,
-) -> Result<Vec<u8>> {
+) -> Result<Vec<u8>>
+where
+    D: Digest,
+    MGD: Digest + FixedOutputReset,
+{
     let h_size = <D as Digest>::output_size();
 
     let label = label.unwrap_or_default();

src/algorithms/pss.rs

@@ -10,20 +10,23 @@
 //! [RFC8017 § 8.1]: https://datatracker.ietf.org/doc/html/rfc8017#section-8.1
 
 use alloc::vec::Vec;
-use digest::{Digest, DynDigest, FixedOutputReset};
+use digest::{Digest, FixedOutputReset};
 use subtle::{Choice, ConditionallySelectable, ConstantTimeEq};
 
 use super::mgf::{mgf1_xor, mgf1_xor_digest};
 use crate::errors::{Error, Result};
 
-pub(crate) fn emsa_pss_encode(
+pub(crate) fn emsa_pss_encode<D>(
     m_hash: &[u8],
     em_bits: usize,
     salt: &[u8],
-    hash: &mut dyn DynDigest,
-) -> Result<Vec<u8>> {
+    hash: &mut D,
+) -> Result<Vec<u8>>
+where
+    D: Digest + FixedOutputReset,
+{
     // See [1], section 9.1.1
-    let h_len = hash.output_size();
+    let h_len = <D as Digest>::output_size();
     let s_len = salt.len();
     let em_len = em_bits.div_ceil(8);
 
@@ -59,9 +62,9 @@ pub(crate) fn emsa_pss_encode(
     // 6.  Let H = Hash(M'), an octet string of length h_len.
     let prefix = [0u8; 8];
 
-    hash.update(&prefix);
-    hash.update(m_hash);
-    hash.update(salt);
+    Digest::update(hash, prefix);
+    Digest::update(hash, m_hash);
+    Digest::update(hash, salt);
 
     let hashed = hash.finalize_reset();
     h.copy_from_slice(&hashed);
@@ -267,17 +270,20 @@ fn emsa_pss_get_salt_len(db: &[u8], em_len: usize, h_len: usize) -> (usize, Choi
     (result_len as usize, final_valid)
 }
 
-pub(crate) fn emsa_pss_verify(
+pub(crate) fn emsa_pss_verify<D>(
     m_hash: &[u8],
     em: &mut [u8],
     s_len: Option<usize>,
-    hash: &mut dyn DynDigest,
+    hash: &mut D,
     key_bits: usize,
-) -> Result<()> {
+) -> Result<()>
+where
+    D: Digest + FixedOutputReset,
+{
     let em_bits = key_bits - 1;
     let em_len = em_bits.div_ceil(8);
     let key_len = key_bits.div_ceil(8);
-    let h_len = hash.output_size();
+    let h_len = <D as Digest>::output_size();
 
     let em = &mut em[key_len - em_len..];
 
@@ -308,13 +314,13 @@ pub(crate) fn emsa_pss_verify(
     // 13. Let H' = Hash(M'), an octet string of length hLen.
     let prefix = [0u8; 8];
 
-    hash.update(&prefix[..]);
-    hash.update(m_hash);
-    hash.update(salt);
+    Digest::update(hash, &prefix[..]);
+    Digest::update(hash, m_hash);
+    Digest::update(hash, salt);
     let h0 = hash.finalize_reset();
 
     // 14. If H = H', output "consistent." Otherwise, output "inconsistent."
-    if (salt_valid & h0.ct_eq(h)).into() {
+    if (salt_valid & h0.as_slice().ct_eq(h)).into() {
         Ok(())
     } else {
         Err(Error::Verification)

src/lib.rs

@@ -34,12 +34,12 @@
 //!
 //! // Encrypt
 //! let data = b"hello world";
-//! let padding = Oaep::new::<Sha256>();
+//! let padding = Oaep::<Sha256>::new();
 //! let enc_data = public_key.encrypt(&mut rng, padding, &data[..]).expect("failed to encrypt");
 //! assert_ne!(&data[..], &enc_data[..]);
 //!
 //! // Decrypt
-//! let padding = Oaep::new::<Sha256>();
+//! let padding = Oaep::<Sha256>::new();
 //! let dec_data = private_key.decrypt(padding, &enc_data).expect("failed to decrypt");
 //! assert_eq!(&data[..], &dec_data[..]);
 //! ```