rust/bssl-crypto/src/hpke.rs - boringssl - Git at Google

 /* Copyright (c) 2024, Google Inc.
  *
  * Permission to use, copy, modify, and/or distribute this software for any
  * purpose with or without fee is hereby granted, provided that the above
  * copyright notice and this permission notice appear in all copies.
  *
  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
  * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
  * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
  * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */

 //! Hybrid Public Key Encryption
 //!
 //! HPKE provides a variant of public key encryption of arbitrary-sized plaintexts
 //! for a recipient public key. It works for any combination of an asymmetric key
 //! encapsulation mechanism (KEM), key derivation function (KDF), and authenticated
 //! encryption with additional data (AEAD) function.
 //!
 //! See RFC 9180 for more details.
 //!
 //! Note that key generation is currently not supported.
 //!
 //! ```
 //! use bssl_crypto::hpke::{Params, RecipientContext, SenderContext};
 //!
 //! let params = Params::new_from_rfc_ids(32, 1, 1).unwrap();
 //! let recipient_pub_key = ...;
 //! let info = ...;
 //! let mut sender_ctx =
 //!     SenderContext::new(&params, &recipient_pub_key, &info).unwrap();
 //!
 //! let pt = b"plaintext";
 //! let ad = b"associated_data";
 //! let ct = sender_ctx.seal(pt, ad);
 //!
 //! let recipient_priv_key = ...;
 //! let mut recipient_ctx = RecipientContext::new(
 //!     &params,
 //!     &recipient_priv_key,
 //!     &sender_ctx.encapsulated_key(),
 //!     &info,
 //! ).unwrap();
 //!
 //! let got_pt = recipient_ctx.open(&ct, ad);
 //! ```

 use crate::{scoped, with_output_vec, with_output_vec_fallible, FfiSlice};
 use alloc::vec::Vec;

 /// Supported KEM algorithms with values detailed in RFC 9180.
 #[derive(PartialEq)]
 #[allow(missing_docs)]
 pub enum Kem {
     X25519HkdfSha256 = 32,
 }

 /// Supported KDF algorithms with values detailed in RFC 9180.
 #[derive(PartialEq)]
 #[allow(missing_docs)]
 pub enum Kdf {
     HkdfSha256 = 1,
 }

 /// Supported AEAD algorithms with values detailed in RFC 9180.
 #[derive(PartialEq)]
 #[allow(missing_docs)]
 pub enum Aead {
     Aes128Gcm = 1,
 }

 /// Maximum length of the encapsulated key for all currently supported KEMs.
 const MAX_ENCAPSULATED_KEY_LEN: usize = bssl_sys::EVP_HPKE_MAX_ENC_LENGTH as usize;

 /// HPKE parameters, including KEM, KDF, and AEAD.
 pub struct Params {
     kem: *const bssl_sys::EVP_HPKE_KEM,
     kdf: *const bssl_sys::EVP_HPKE_KDF,
     aead: *const bssl_sys::EVP_HPKE_AEAD,
 }

 impl Params {
     /// New Params from KEM, KDF, and AEAD enums.
     pub fn new(kem: Kem, kdf: Kdf, aead: Aead) -> Option<Self> {
         if kem != Kem::X25519HkdfSha256 || kdf != Kdf::HkdfSha256 || aead != Aead::Aes128Gcm {
             return None;
         }
         // Safety: EVP_hpke_x25519_hkdf_sha256, EVP_hpke_hkdf_sha256, and EVP_hpke_aes_128_gcm
         // initialize structs containing constants and cannot return an error.
         unsafe {
             Some(Self {
                 kem: bssl_sys::EVP_hpke_x25519_hkdf_sha256() as *const bssl_sys::EVP_HPKE_KEM,
                 kdf: bssl_sys::EVP_hpke_hkdf_sha256() as *const bssl_sys::EVP_HPKE_KDF,
                 aead: bssl_sys::EVP_hpke_aes_128_gcm() as *const bssl_sys::EVP_HPKE_AEAD,
             })
         }
     }

     /// New Params from KEM, KDF, and AEAD IDs as detailed in RFC 9180.
     pub fn new_from_rfc_ids(kem: u16, kdf: u16, aead: u16) -> Option<Self> {
         if kem != Kem::X25519HkdfSha256 as u16
             || kdf != Kdf::HkdfSha256 as u16
             || aead != Aead::Aes128Gcm as u16
         {
             return None;
         }
         // Safety: EVP_hpke_x25519_hkdf_sha256, EVP_hpke_hkdf_sha256, and EVP_hpke_aes_128_gcm
         // initialize structs containing constants and cannot return an error.
         unsafe {
             Some(Self {
                 kem: bssl_sys::EVP_hpke_x25519_hkdf_sha256() as *const bssl_sys::EVP_HPKE_KEM,
                 kdf: bssl_sys::EVP_hpke_hkdf_sha256() as *const bssl_sys::EVP_HPKE_KDF,
                 aead: bssl_sys::EVP_hpke_aes_128_gcm() as *const bssl_sys::EVP_HPKE_AEAD,
             })
         }
     }
 }

 /// HPKE recipient context. Callers may use `open()` to decrypt messages from the sender.
 pub struct RecipientContext {
     ctx: scoped::EvpHpkeCtx,
 }

 /// HPKE sender context. Callers may use `seal()` to encrypt messages for the recipient.
 pub struct SenderContext {
     ctx: RecipientContext,
     encapsulated_key: Vec<u8>,
 }

 impl SenderContext {
     /// New implements the SetupBaseS HPKE operation, which encapsulates a shared secret for
     /// `recipient_pub_key` and sets up a sender context. These are stored and returned in the
     /// newly created SenderContext.
     ///
     /// Note that `recipient_pub_key` may be invalid, in which case this function will return an
     /// error.
     ///
     /// On success, callers may use `seal()` to encrypt messages for the recipient.
     pub fn new(params: &Params, recipient_pub_key: &[u8], info: &[u8]) -> Option<Self> {
         let mut ctx = scoped::EvpHpkeCtx::new();
         unsafe {
             with_output_vec_fallible(MAX_ENCAPSULATED_KEY_LEN, |enc_key_buf| {
                 let mut enc_key_len = 0usize;
                 // Safety: EVP_HPKE_CTX_setup_sender
                 // - is called with context created from EVP_HPKE_CTX_new,
                 // - is called with valid buffers with corresponding pointer and length, and
                 // - returns 0 on error.
                 let result = bssl_sys::EVP_HPKE_CTX_setup_sender(
                     ctx.as_mut_ffi_ptr(),
                     enc_key_buf,
                     &mut enc_key_len,
                     MAX_ENCAPSULATED_KEY_LEN,
                     params.kem,
                     params.kdf,
                     params.aead,
                     recipient_pub_key.as_ffi_ptr(),
                     recipient_pub_key.len(),
                     info.as_ffi_ptr(),
                     info.len(),
                 );
                 if result == 1 {
                     Some(enc_key_len)
                 } else {
                     None
                 }
             })
         }
         .map(|enc_key| Self {
             ctx: RecipientContext { ctx },
             encapsulated_key: enc_key,
         })
     }

     /// Seal encrypts `pt` and returns the resulting ciphertext, which is authenticated with `aad`.
     ///
     /// Note that HPKE encryption is stateful and ordered. The sender's first call to `seal()` must
     /// correspond to the recipient's first call to `open()`, etc.
     ///
     /// This function panics if adding the `pt` length and bssl_sys::EVP_HPKE_CTX_max_overhead
     /// overflows.
     pub fn seal(&mut self, pt: &[u8], aad: &[u8]) -> Vec<u8> {
         self.ctx.seal(pt, aad)
     }

     #[allow(missing_docs)]
     pub fn encapsulated_key(&self) -> &[u8] {
         &self.encapsulated_key
     }
 }

 impl RecipientContext {
     /// New implements the SetupBaseR HPKE operation, which decapsulates the shared secret in
     /// `encapsulated_key` with `recipient_priv_key` and sets up a recipient context. These are
     /// stored and returned in the newly created RecipientContext.
     ///
     /// Note that `encapsulated_key` may be invalid, in which case this function will return an
     /// error.
     ///
     /// On success, callers may use `open()` to decrypt messages from the sender.
     pub fn new(
         params: &Params,
         recipient_priv_key: &[u8],
         encapsulated_key: &[u8],
         info: &[u8],
     ) -> Option<Self> {
         let mut hpke_key = scoped::EvpHpkeKey::new();

         // Safety: EVP_HPKE_KEY_init returns 0 on error.
         let result = unsafe {
             bssl_sys::EVP_HPKE_KEY_init(
                 hpke_key.as_mut_ffi_ptr(),
                 params.kem,
                 recipient_priv_key.as_ffi_ptr(),
                 recipient_priv_key.len(),
             )
         };
         if result != 1 {
             return None;
         }

         let mut ctx = scoped::EvpHpkeCtx::new();

         // Safety: EVP_HPKE_CTX_setup_recipient
         // - is called with context created from EVP_HPKE_CTX_new,
         // - is called with HPKE key created from EVP_HPKE_KEY_init,
         // - is called with valid buffers with corresponding pointer and length, and
         // - returns 0 on error.
         let result = unsafe {
             bssl_sys::EVP_HPKE_CTX_setup_recipient(
                 ctx.as_mut_ffi_ptr(),
                 hpke_key.as_ffi_ptr(),
                 params.kdf,
                 params.aead,
                 encapsulated_key.as_ffi_ptr(),
                 encapsulated_key.len(),
                 info.as_ffi_ptr(),
                 info.len(),
             )
         };
         if result == 1 {
             Some(Self { ctx })
         } else {
             None
         }
     }

     /// Seal encrypts `pt` and returns the resulting ciphertext, which is authenticated with `aad`.
     ///
     /// Note that HPKE encryption is stateful and ordered. The sender's first call to `seal()` must
     /// correspond to the recipient's first call to `open()`, etc.
     ///
     /// This function panics if adding the `pt` length and bssl_sys::EVP_HPKE_CTX_max_overhead
     /// overflows.
     pub fn seal(&mut self, pt: &[u8], aad: &[u8]) -> Vec<u8> {
         // Safety: EVP_HPKE_CTX_max_overhead panics if ctx is not set up as a sender.
         #[allow(clippy::expect_used)]
         let max_out_len = pt
             .len()
             .checked_add(unsafe { bssl_sys::EVP_HPKE_CTX_max_overhead(self.ctx.as_mut_ffi_ptr()) })
             .expect("Maximum output length calculation overflow");
         unsafe {
             with_output_vec(max_out_len, |out_buf| {
                 let mut out_len = 0usize;
                 // Safety: EVP_HPKE_CTX_seal
                 // - is called with context created from EVP_HPKE_CTX_new and
                 // - is called with valid buffers with corresponding pointer and length.
                 let result = bssl_sys::EVP_HPKE_CTX_seal(
                     self.ctx.as_mut_ffi_ptr(),
                     out_buf,
                     &mut out_len,
                     max_out_len,
                     pt.as_ffi_ptr(),
                     pt.len(),
                     aad.as_ffi_ptr(),
                     aad.len(),
                 );
                 assert_eq!(result, 1);
                 out_len
             })
         }
     }

     /// Open authenticates `aad` and decrypts `ct`. It returns an error on failure.
     ///
     /// Note that HPKE encryption is stateful and ordered. The sender's first call to `seal()` must
     /// correspond to the recipient's first call to `open()`, etc.
     pub fn open(&mut self, ct: &[u8], aad: &[u8]) -> Option<Vec<u8>> {
         let max_out_len = ct.len();
         unsafe {
             with_output_vec_fallible(max_out_len, |out_buf| {
                 let mut out_len = 0usize;
                 // Safety: EVP_HPKE_CTX_open
                 // - is called with context created from EVP_HPKE_CTX_new and
                 // - is called with valid buffers with corresponding pointer and length.
                 let result = bssl_sys::EVP_HPKE_CTX_open(
                     self.ctx.as_mut_ffi_ptr(),
                     out_buf,
                     &mut out_len,
                     max_out_len,
                     ct.as_ffi_ptr(),
                     ct.len(),
                     aad.as_ffi_ptr(),
                     aad.len(),
                 );
                 if result == 1 {
                     Some(out_len)
                 } else {
                     None
                 }
             })
         }
     }
 }

 #[cfg(test)]
 mod test {
     use super::*;
     use crate::test_helpers::decode_hex;

     struct TestVector {
         kem_id: u16,
         kdf_id: u16,
         aead_id: u16,
         info: [u8; 20],
         seed_for_testing: [u8; 32],   // skEm
         recipient_pub_key: [u8; 32],  // pkRm
         recipient_priv_key: [u8; 32], // skRm
         encapsulated_key: [u8; 32],   // enc
         plaintext: [u8; 29],          // pt
         associated_data: [u8; 7],     // aad
         ciphertext: [u8; 45],         // ct
     }

     // https://www.rfc-editor.org/rfc/rfc9180.html#appendix-A.1
     fn x25519_hkdf_sha256_hkdf_sha256_aes_128_gcm() -> TestVector {
         TestVector {
             kem_id: 32,
             kdf_id: 1,
             aead_id: 1,
             info: decode_hex("4f6465206f6e2061204772656369616e2055726e"),
             seed_for_testing: decode_hex("52c4a758a802cd8b936eceea314432798d5baf2d7e9235dc084ab1b9cfa2f736"),
             recipient_pub_key: decode_hex("3948cfe0ad1ddb695d780e59077195da6c56506b027329794ab02bca80815c4d"),
             recipient_priv_key: decode_hex("4612c550263fc8ad58375df3f557aac531d26850903e55a9f23f21d8534e8ac8"),
             encapsulated_key: decode_hex("37fda3567bdbd628e88668c3c8d7e97d1d1253b6d4ea6d44c150f741f1bf4431"),
             plaintext: decode_hex("4265617574792069732074727574682c20747275746820626561757479"),
             associated_data: decode_hex("436f756e742d30"),
             ciphertext: decode_hex("f938558b5d72f1a23810b4be2ab4f84331acc02fc97babc53a52ae8218a355a96d8770ac83d07bea87e13c512a"),
         }
     }

     #[test]
     fn seal_and_open() {
         let vec: TestVector = x25519_hkdf_sha256_hkdf_sha256_aes_128_gcm();
         let params = Params::new_from_rfc_ids(vec.kem_id, vec.kdf_id, vec.aead_id).unwrap();

         let mut sender_ctx =
             SenderContext::new(&params, &vec.recipient_pub_key, &vec.info).unwrap();

         let mut recipient_ctx = RecipientContext::new(
             &params,
             &vec.recipient_priv_key,
             &sender_ctx.encapsulated_key(),
             &vec.info,
         )
         .unwrap();

         let pt = b"plaintext";
         let ad = b"associated_data";
         let mut prev_ct: Vec<u8> = Vec::new();
         for _ in 0..10 {
             let ct = sender_ctx.seal(pt, ad);
             assert_ne!(ct, prev_ct);
             prev_ct = ct.clone();

             let got_pt = recipient_ctx.open(&ct, ad).unwrap();
             assert_eq!(got_pt, pt);
         }
     }

     fn new_sender_context_for_testing(
         params: &Params,
         recipient_pub_key: &[u8],
         info: &[u8],
         seed_for_testing: &[u8],
     ) -> Option<SenderContext> {
         let mut ctx = scoped::EvpHpkeCtx::new();

         unsafe {
             with_output_vec_fallible(MAX_ENCAPSULATED_KEY_LEN, |enc_key_buf| {
                 let mut enc_key_len = 0usize;
                 // Safety: EVP_HPKE_CTX_setup_sender_with_seed_for_testing
                 // - is called with context created from EVP_HPKE_CTX_new,
                 // - is called with valid buffers with corresponding pointer and length, and
                 // - returns 0 on error.
                 let result = bssl_sys::EVP_HPKE_CTX_setup_sender_with_seed_for_testing(
                     ctx.as_mut_ffi_ptr(),
                     enc_key_buf,
                     &mut enc_key_len,
                     MAX_ENCAPSULATED_KEY_LEN,
                     params.kem,
                     params.kdf,
                     params.aead,
                     recipient_pub_key.as_ffi_ptr(),
                     recipient_pub_key.len(),
                     info.as_ffi_ptr(),
                     info.len(),
                     seed_for_testing.as_ffi_ptr(),
                     seed_for_testing.len(),
                 );
                 if result == 1 {
                     Some(enc_key_len)
                 } else {
                     None
                 }
             })
         }
         .map(|enc_key| SenderContext {
             ctx: RecipientContext { ctx },
             encapsulated_key: enc_key,
         })
     }

     #[test]
     fn seal_with_vector() {
         let vec: TestVector = x25519_hkdf_sha256_hkdf_sha256_aes_128_gcm();
         let params = Params::new_from_rfc_ids(vec.kem_id, vec.kdf_id, vec.aead_id).unwrap();

         let mut ctx = new_sender_context_for_testing(
             &params,
             &vec.recipient_pub_key,
             &vec.info,
             &vec.seed_for_testing,
         )
         .unwrap();

         assert_eq!(ctx.encapsulated_key, vec.encapsulated_key.to_vec());

         let ciphertext = ctx.seal(&vec.plaintext, &vec.associated_data);
         assert_eq!(ciphertext, vec.ciphertext.to_vec());
     }

     #[test]
     fn open_with_vector() {
         let vec: TestVector = x25519_hkdf_sha256_hkdf_sha256_aes_128_gcm();
         let params = Params::new_from_rfc_ids(vec.kem_id, vec.kdf_id, vec.aead_id).unwrap();

         let mut ctx = RecipientContext::new(
             &params,
             &vec.recipient_priv_key,
             &vec.encapsulated_key,
             &vec.info,
         )
         .unwrap();

         let plaintext = ctx.open(&vec.ciphertext, &vec.associated_data).unwrap();
         assert_eq!(plaintext, vec.plaintext.to_vec());
     }

     #[test]
     fn params_new() {
         assert!(Params::new(Kem::X25519HkdfSha256, Kdf::HkdfSha256, Aead::Aes128Gcm).is_some());
     }

     #[test]
     fn params_new_from_rfc_ids() {
         let vec: TestVector = x25519_hkdf_sha256_hkdf_sha256_aes_128_gcm();
         assert!(Params::new_from_rfc_ids(vec.kem_id, vec.kdf_id, vec.aead_id).is_some());
     }

     #[test]
     fn disallowed_params_fail() {
         let vec: TestVector = x25519_hkdf_sha256_hkdf_sha256_aes_128_gcm();

         assert!(Params::new_from_rfc_ids(0, vec.kdf_id, vec.aead_id).is_none());
         assert!(Params::new_from_rfc_ids(vec.kem_id, 0, vec.aead_id).is_none());
         assert!(Params::new_from_rfc_ids(vec.kem_id, vec.kdf_id, 0).is_none());
         assert!(Params::new_from_rfc_ids(
             vec.kem_id,
             vec.kdf_id,
             bssl_sys::EVP_HPKE_AES_256_GCM as u16
         )
         .is_none());
     }

     #[test]
     fn bad_recipient_pub_key_fails() {
         let vec: TestVector = x25519_hkdf_sha256_hkdf_sha256_aes_128_gcm();
         let params = Params::new_from_rfc_ids(vec.kem_id, vec.kdf_id, vec.aead_id).unwrap();

         assert!(SenderContext::new(&params, b"", &vec.info).is_none());
     }

     #[test]
     fn bad_recipient_priv_key_fails() {
         let vec: TestVector = x25519_hkdf_sha256_hkdf_sha256_aes_128_gcm();
         let params = Params::new_from_rfc_ids(vec.kem_id, vec.kdf_id, vec.aead_id).unwrap();

         assert!(RecipientContext::new(&params, b"", &vec.encapsulated_key, &vec.info).is_none());
     }
 }
	/* Copyright (c) 2024, Google Inc.
	*
	* Permission to use, copy, modify, and/or distribute this software for any
	* purpose with or without fee is hereby granted, provided that the above
	* copyright notice and this permission notice appear in all copies.
	*
	* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
	* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
	* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
	* SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
	* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
	* OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
	* CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
	*/

	//! Hybrid Public Key Encryption
	//!
	//! HPKE provides a variant of public key encryption of arbitrary-sized plaintexts
	//! for a recipient public key. It works for any combination of an asymmetric key
	//! encapsulation mechanism (KEM), key derivation function (KDF), and authenticated
	//! encryption with additional data (AEAD) function.
	//!
	//! See RFC 9180 for more details.
	//!
	//! Note that key generation is currently not supported.
	//!
	//! ```
	//! use bssl_crypto::hpke::{Params, RecipientContext, SenderContext};
	//!
	//! let params = Params::new_from_rfc_ids(32, 1, 1).unwrap();
	//! let recipient_pub_key = ...;
	//! let info = ...;
	//! let mut sender_ctx =
	//! SenderContext::new(&params, &recipient_pub_key, &info).unwrap();
	//!
	//! let pt = b"plaintext";
	//! let ad = b"associated_data";
	//! let ct = sender_ctx.seal(pt, ad);
	//!
	//! let recipient_priv_key = ...;
	//! let mut recipient_ctx = RecipientContext::new(
	//! &params,
	//! &recipient_priv_key,
	//! &sender_ctx.encapsulated_key(),
	//! &info,
	//! ).unwrap();
	//!
	//! let got_pt = recipient_ctx.open(&ct, ad);
	//! ```

	use crate::{scoped, with_output_vec, with_output_vec_fallible, FfiSlice};
	use alloc::vec::Vec;

	/// Supported KEM algorithms with values detailed in RFC 9180.
	#[derive(PartialEq)]
	#[allow(missing_docs)]
	pub enum Kem {
	X25519HkdfSha256 = 32,
	}

	/// Supported KDF algorithms with values detailed in RFC 9180.
	#[derive(PartialEq)]
	#[allow(missing_docs)]
	pub enum Kdf {
	HkdfSha256 = 1,
	}

	/// Supported AEAD algorithms with values detailed in RFC 9180.
	#[derive(PartialEq)]
	#[allow(missing_docs)]
	pub enum Aead {
	Aes128Gcm = 1,
	}

	/// Maximum length of the encapsulated key for all currently supported KEMs.
	const MAX_ENCAPSULATED_KEY_LEN: usize = bssl_sys::EVP_HPKE_MAX_ENC_LENGTH as usize;

	/// HPKE parameters, including KEM, KDF, and AEAD.
	pub struct Params {
	kem: *const bssl_sys::EVP_HPKE_KEM,
	kdf: *const bssl_sys::EVP_HPKE_KDF,
	aead: *const bssl_sys::EVP_HPKE_AEAD,
	}

	impl Params {
	/// New Params from KEM, KDF, and AEAD enums.
	pub fn new(kem: Kem, kdf: Kdf, aead: Aead) -> Option<Self> {
	if kem != Kem::X25519HkdfSha256 \|\| kdf != Kdf::HkdfSha256 \|\| aead != Aead::Aes128Gcm {
	return None;
	}
	// Safety: EVP_hpke_x25519_hkdf_sha256, EVP_hpke_hkdf_sha256, and EVP_hpke_aes_128_gcm
	// initialize structs containing constants and cannot return an error.
	unsafe {
	Some(Self {
	kem: bssl_sys::EVP_hpke_x25519_hkdf_sha256() as *const bssl_sys::EVP_HPKE_KEM,
	kdf: bssl_sys::EVP_hpke_hkdf_sha256() as *const bssl_sys::EVP_HPKE_KDF,
	aead: bssl_sys::EVP_hpke_aes_128_gcm() as *const bssl_sys::EVP_HPKE_AEAD,
	})
	}
	}

	/// New Params from KEM, KDF, and AEAD IDs as detailed in RFC 9180.
	pub fn new_from_rfc_ids(kem: u16, kdf: u16, aead: u16) -> Option<Self> {
	if kem != Kem::X25519HkdfSha256 as u16
	\|\| kdf != Kdf::HkdfSha256 as u16
	\|\| aead != Aead::Aes128Gcm as u16
	{
	return None;
	}
	// Safety: EVP_hpke_x25519_hkdf_sha256, EVP_hpke_hkdf_sha256, and EVP_hpke_aes_128_gcm
	// initialize structs containing constants and cannot return an error.
	unsafe {
	Some(Self {
	kem: bssl_sys::EVP_hpke_x25519_hkdf_sha256() as *const bssl_sys::EVP_HPKE_KEM,
	kdf: bssl_sys::EVP_hpke_hkdf_sha256() as *const bssl_sys::EVP_HPKE_KDF,
	aead: bssl_sys::EVP_hpke_aes_128_gcm() as *const bssl_sys::EVP_HPKE_AEAD,
	})
	}
	}
	}

	/// HPKE recipient context. Callers may use `open()` to decrypt messages from the sender.
	pub struct RecipientContext {
	ctx: scoped::EvpHpkeCtx,
	}

	/// HPKE sender context. Callers may use `seal()` to encrypt messages for the recipient.
	pub struct SenderContext {
	ctx: RecipientContext,
	encapsulated_key: Vec<u8>,
	}

	impl SenderContext {
	/// New implements the SetupBaseS HPKE operation, which encapsulates a shared secret for
	/// `recipient_pub_key` and sets up a sender context. These are stored and returned in the
	/// newly created SenderContext.
	///
	/// Note that `recipient_pub_key` may be invalid, in which case this function will return an
	/// error.
	///
	/// On success, callers may use `seal()` to encrypt messages for the recipient.
	pub fn new(params: &Params, recipient_pub_key: &[u8], info: &[u8]) -> Option<Self> {
	let mut ctx = scoped::EvpHpkeCtx::new();
	unsafe {
	with_output_vec_fallible(MAX_ENCAPSULATED_KEY_LEN, \|enc_key_buf\| {
	let mut enc_key_len = 0usize;
	// Safety: EVP_HPKE_CTX_setup_sender
	// - is called with context created from EVP_HPKE_CTX_new,
	// - is called with valid buffers with corresponding pointer and length, and
	// - returns 0 on error.
	let result = bssl_sys::EVP_HPKE_CTX_setup_sender(
	ctx.as_mut_ffi_ptr(),
	enc_key_buf,
	&mut enc_key_len,
	MAX_ENCAPSULATED_KEY_LEN,
	params.kem,
	params.kdf,
	params.aead,
	recipient_pub_key.as_ffi_ptr(),
	recipient_pub_key.len(),
	info.as_ffi_ptr(),
	info.len(),
	);
	if result == 1 {
	Some(enc_key_len)
	} else {
	None
	}
	})
	}
	.map(\|enc_key\| Self {
	ctx: RecipientContext { ctx },
	encapsulated_key: enc_key,
	})
	}

	/// Seal encrypts `pt` and returns the resulting ciphertext, which is authenticated with `aad`.
	///
	/// Note that HPKE encryption is stateful and ordered. The sender's first call to `seal()` must
	/// correspond to the recipient's first call to `open()`, etc.
	///
	/// This function panics if adding the `pt` length and bssl_sys::EVP_HPKE_CTX_max_overhead
	/// overflows.
	pub fn seal(&mut self, pt: &[u8], aad: &[u8]) -> Vec<u8> {
	self.ctx.seal(pt, aad)
	}

	#[allow(missing_docs)]
	pub fn encapsulated_key(&self) -> &[u8] {
	&self.encapsulated_key
	}
	}

	impl RecipientContext {
	/// New implements the SetupBaseR HPKE operation, which decapsulates the shared secret in
	/// `encapsulated_key` with `recipient_priv_key` and sets up a recipient context. These are
	/// stored and returned in the newly created RecipientContext.
	///
	/// Note that `encapsulated_key` may be invalid, in which case this function will return an
	/// error.
	///
	/// On success, callers may use `open()` to decrypt messages from the sender.
	pub fn new(
	params: &Params,
	recipient_priv_key: &[u8],
	encapsulated_key: &[u8],
	info: &[u8],
	) -> Option<Self> {
	let mut hpke_key = scoped::EvpHpkeKey::new();

	// Safety: EVP_HPKE_KEY_init returns 0 on error.
	let result = unsafe {
	bssl_sys::EVP_HPKE_KEY_init(
	hpke_key.as_mut_ffi_ptr(),
	params.kem,
	recipient_priv_key.as_ffi_ptr(),
	recipient_priv_key.len(),
	)
	};
	if result != 1 {
	return None;
	}

	let mut ctx = scoped::EvpHpkeCtx::new();

	// Safety: EVP_HPKE_CTX_setup_recipient
	// - is called with context created from EVP_HPKE_CTX_new,
	// - is called with HPKE key created from EVP_HPKE_KEY_init,
	// - is called with valid buffers with corresponding pointer and length, and
	// - returns 0 on error.
	let result = unsafe {
	bssl_sys::EVP_HPKE_CTX_setup_recipient(
	ctx.as_mut_ffi_ptr(),
	hpke_key.as_ffi_ptr(),
	params.kdf,
	params.aead,
	encapsulated_key.as_ffi_ptr(),
	encapsulated_key.len(),
	info.as_ffi_ptr(),
	info.len(),
	)
	};
	if result == 1 {
	Some(Self { ctx })
	} else {
	None
	}
	}

	/// Seal encrypts `pt` and returns the resulting ciphertext, which is authenticated with `aad`.
	///
	/// Note that HPKE encryption is stateful and ordered. The sender's first call to `seal()` must
	/// correspond to the recipient's first call to `open()`, etc.
	///
	/// This function panics if adding the `pt` length and bssl_sys::EVP_HPKE_CTX_max_overhead
	/// overflows.
	pub fn seal(&mut self, pt: &[u8], aad: &[u8]) -> Vec<u8> {
	// Safety: EVP_HPKE_CTX_max_overhead panics if ctx is not set up as a sender.
	#[allow(clippy::expect_used)]
	let max_out_len = pt
	.len()
	.checked_add(unsafe { bssl_sys::EVP_HPKE_CTX_max_overhead(self.ctx.as_mut_ffi_ptr()) })
	.expect("Maximum output length calculation overflow");
	unsafe {
	with_output_vec(max_out_len, \|out_buf\| {
	let mut out_len = 0usize;
	// Safety: EVP_HPKE_CTX_seal
	// - is called with context created from EVP_HPKE_CTX_new and
	// - is called with valid buffers with corresponding pointer and length.
	let result = bssl_sys::EVP_HPKE_CTX_seal(
	self.ctx.as_mut_ffi_ptr(),
	out_buf,
	&mut out_len,
	max_out_len,
	pt.as_ffi_ptr(),
	pt.len(),
	aad.as_ffi_ptr(),
	aad.len(),
	);
	assert_eq!(result, 1);
	out_len
	})
	}
	}

	/// Open authenticates `aad` and decrypts `ct`. It returns an error on failure.
	///
	/// Note that HPKE encryption is stateful and ordered. The sender's first call to `seal()` must
	/// correspond to the recipient's first call to `open()`, etc.
	pub fn open(&mut self, ct: &[u8], aad: &[u8]) -> Option<Vec<u8>> {
	let max_out_len = ct.len();
	unsafe {
	with_output_vec_fallible(max_out_len, \|out_buf\| {
	let mut out_len = 0usize;
	// Safety: EVP_HPKE_CTX_open
	// - is called with context created from EVP_HPKE_CTX_new and
	// - is called with valid buffers with corresponding pointer and length.
	let result = bssl_sys::EVP_HPKE_CTX_open(
	self.ctx.as_mut_ffi_ptr(),
	out_buf,
	&mut out_len,
	max_out_len,
	ct.as_ffi_ptr(),
	ct.len(),
	aad.as_ffi_ptr(),
	aad.len(),
	);
	if result == 1 {
	Some(out_len)
	} else {
	None
	}
	})
	}
	}
	}

	#[cfg(test)]
	mod test {
	use super::*;
	use crate::test_helpers::decode_hex;

	struct TestVector {
	kem_id: u16,
	kdf_id: u16,
	aead_id: u16,
	info: [u8; 20],
	seed_for_testing: [u8; 32], // skEm
	recipient_pub_key: [u8; 32], // pkRm
	recipient_priv_key: [u8; 32], // skRm
	encapsulated_key: [u8; 32], // enc
	plaintext: [u8; 29], // pt
	associated_data: [u8; 7], // aad
	ciphertext: [u8; 45], // ct
	}

	// https://www.rfc-editor.org/rfc/rfc9180.html#appendix-A.1
	fn x25519_hkdf_sha256_hkdf_sha256_aes_128_gcm() -> TestVector {
	TestVector {
	kem_id: 32,
	kdf_id: 1,
	aead_id: 1,
	info: decode_hex("4f6465206f6e2061204772656369616e2055726e"),
	seed_for_testing: decode_hex("52c4a758a802cd8b936eceea314432798d5baf2d7e9235dc084ab1b9cfa2f736"),
	recipient_pub_key: decode_hex("3948cfe0ad1ddb695d780e59077195da6c56506b027329794ab02bca80815c4d"),
	recipient_priv_key: decode_hex("4612c550263fc8ad58375df3f557aac531d26850903e55a9f23f21d8534e8ac8"),
	encapsulated_key: decode_hex("37fda3567bdbd628e88668c3c8d7e97d1d1253b6d4ea6d44c150f741f1bf4431"),
	plaintext: decode_hex("4265617574792069732074727574682c20747275746820626561757479"),
	associated_data: decode_hex("436f756e742d30"),
	ciphertext: decode_hex("f938558b5d72f1a23810b4be2ab4f84331acc02fc97babc53a52ae8218a355a96d8770ac83d07bea87e13c512a"),
	}
	}

	#[test]
	fn seal_and_open() {
	let vec: TestVector = x25519_hkdf_sha256_hkdf_sha256_aes_128_gcm();
	let params = Params::new_from_rfc_ids(vec.kem_id, vec.kdf_id, vec.aead_id).unwrap();

	let mut sender_ctx =
	SenderContext::new(&params, &vec.recipient_pub_key, &vec.info).unwrap();

	let mut recipient_ctx = RecipientContext::new(
	&params,
	&vec.recipient_priv_key,
	&sender_ctx.encapsulated_key(),
	&vec.info,
	)
	.unwrap();

	let pt = b"plaintext";
	let ad = b"associated_data";
	let mut prev_ct: Vec<u8> = Vec::new();
	for _ in 0..10 {
	let ct = sender_ctx.seal(pt, ad);
	assert_ne!(ct, prev_ct);
	prev_ct = ct.clone();

	let got_pt = recipient_ctx.open(&ct, ad).unwrap();
	assert_eq!(got_pt, pt);
	}
	}

	fn new_sender_context_for_testing(
	params: &Params,
	recipient_pub_key: &[u8],
	info: &[u8],
	seed_for_testing: &[u8],
	) -> Option<SenderContext> {
	let mut ctx = scoped::EvpHpkeCtx::new();

	unsafe {
	with_output_vec_fallible(MAX_ENCAPSULATED_KEY_LEN, \|enc_key_buf\| {
	let mut enc_key_len = 0usize;
	// Safety: EVP_HPKE_CTX_setup_sender_with_seed_for_testing
	// - is called with context created from EVP_HPKE_CTX_new,
	// - is called with valid buffers with corresponding pointer and length, and
	// - returns 0 on error.
	let result = bssl_sys::EVP_HPKE_CTX_setup_sender_with_seed_for_testing(
	ctx.as_mut_ffi_ptr(),
	enc_key_buf,
	&mut enc_key_len,
	MAX_ENCAPSULATED_KEY_LEN,
	params.kem,
	params.kdf,
	params.aead,
	recipient_pub_key.as_ffi_ptr(),
	recipient_pub_key.len(),
	info.as_ffi_ptr(),
	info.len(),
	seed_for_testing.as_ffi_ptr(),
	seed_for_testing.len(),
	);
	if result == 1 {
	Some(enc_key_len)
	} else {
	None
	}
	})
	}
	.map(\|enc_key\| SenderContext {
	ctx: RecipientContext { ctx },
	encapsulated_key: enc_key,
	})
	}

	#[test]
	fn seal_with_vector() {
	let vec: TestVector = x25519_hkdf_sha256_hkdf_sha256_aes_128_gcm();
	let params = Params::new_from_rfc_ids(vec.kem_id, vec.kdf_id, vec.aead_id).unwrap();

	let mut ctx = new_sender_context_for_testing(
	&params,
	&vec.recipient_pub_key,
	&vec.info,
	&vec.seed_for_testing,
	)
	.unwrap();

	assert_eq!(ctx.encapsulated_key, vec.encapsulated_key.to_vec());

	let ciphertext = ctx.seal(&vec.plaintext, &vec.associated_data);
	assert_eq!(ciphertext, vec.ciphertext.to_vec());
	}

	#[test]
	fn open_with_vector() {
	let vec: TestVector = x25519_hkdf_sha256_hkdf_sha256_aes_128_gcm();
	let params = Params::new_from_rfc_ids(vec.kem_id, vec.kdf_id, vec.aead_id).unwrap();

	let mut ctx = RecipientContext::new(
	&params,
	&vec.recipient_priv_key,
	&vec.encapsulated_key,
	&vec.info,
	)
	.unwrap();

	let plaintext = ctx.open(&vec.ciphertext, &vec.associated_data).unwrap();
	assert_eq!(plaintext, vec.plaintext.to_vec());
	}

	#[test]
	fn params_new() {
	assert!(Params::new(Kem::X25519HkdfSha256, Kdf::HkdfSha256, Aead::Aes128Gcm).is_some());
	}

	#[test]
	fn params_new_from_rfc_ids() {
	let vec: TestVector = x25519_hkdf_sha256_hkdf_sha256_aes_128_gcm();
	assert!(Params::new_from_rfc_ids(vec.kem_id, vec.kdf_id, vec.aead_id).is_some());
	}

	#[test]
	fn disallowed_params_fail() {
	let vec: TestVector = x25519_hkdf_sha256_hkdf_sha256_aes_128_gcm();

	assert!(Params::new_from_rfc_ids(0, vec.kdf_id, vec.aead_id).is_none());
	assert!(Params::new_from_rfc_ids(vec.kem_id, 0, vec.aead_id).is_none());
	assert!(Params::new_from_rfc_ids(vec.kem_id, vec.kdf_id, 0).is_none());
	assert!(Params::new_from_rfc_ids(
	vec.kem_id,
	vec.kdf_id,
	bssl_sys::EVP_HPKE_AES_256_GCM as u16
	)
	.is_none());
	}

	#[test]
	fn bad_recipient_pub_key_fails() {
	let vec: TestVector = x25519_hkdf_sha256_hkdf_sha256_aes_128_gcm();
	let params = Params::new_from_rfc_ids(vec.kem_id, vec.kdf_id, vec.aead_id).unwrap();

	assert!(SenderContext::new(&params, b"", &vec.info).is_none());
	}

	#[test]
	fn bad_recipient_priv_key_fails() {
	let vec: TestVector = x25519_hkdf_sha256_hkdf_sha256_aes_128_gcm();
	let params = Params::new_from_rfc_ids(vec.kem_id, vec.kdf_id, vec.aead_id).unwrap();

	assert!(RecipientContext::new(&params, b"", &vec.encapsulated_key, &vec.info).is_none());
	}
	}