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/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
use crate::{
error::{JwCryptoError, Result},
Algorithm, CompactJwe, DecryptionParameters, EncryptionAlgorithm, EncryptionParameters,
JweHeader, Jwk, JwkKeyParameters,
};
use rc_crypto::{
aead,
agreement::{self, EphemeralKeyPair, InputKeyMaterial, UnparsedPublicKey},
digest, rand,
};
use serde_derive::{Deserialize, Serialize};
#[derive(Serialize, Deserialize, Clone, Debug, PartialEq)]
pub struct ECKeysParameters {
pub crv: String,
pub x: String,
pub y: String,
}
pub(crate) fn encrypt_to_jwe(
data: &[u8],
encryption_params: EncryptionParameters,
) -> Result<CompactJwe> {
let EncryptionParameters::ECDH_ES { enc, peer_jwk } = encryption_params;
let local_key_pair = EphemeralKeyPair::generate(&agreement::ECDH_P256)?;
let local_public_key = extract_pub_key_jwk(&local_key_pair)?;
let JwkKeyParameters::EC(ref ec_key_params) = peer_jwk.key_parameters;
let protected_header = JweHeader {
kid: peer_jwk.kid.clone(),
alg: Algorithm::ECDH_ES,
enc,
epk: Some(local_public_key),
apu: None,
apv: None,
};
let secret = derive_shared_secret(&protected_header, local_key_pair, &ec_key_params)?;
let encryption_algorithm = match protected_header.enc {
EncryptionAlgorithm::A256GCM => &aead::AES_256_GCM,
};
let sealing_key = aead::SealingKey::new(encryption_algorithm, &secret.as_ref())?;
let additional_data = serde_json::to_string(&protected_header)?;
let additional_data =
base64::encode_config(additional_data.as_bytes(), base64::URL_SAFE_NO_PAD);
let additional_data = additional_data.as_bytes();
let aad = aead::Aad::from(additional_data);
let mut iv: Vec<u8> = vec![0; 12];
rand::fill(&mut iv)?;
let nonce = aead::Nonce::try_assume_unique_for_key(encryption_algorithm, &iv)?;
let mut encrypted = aead::seal(&sealing_key, nonce, aad, data)?;
let tag_idx = encrypted.len() - encryption_algorithm.tag_len();
let auth_tag = encrypted.split_off(tag_idx);
let ciphertext = encrypted;
Ok(CompactJwe::new(
Some(protected_header),
None,
Some(iv),
ciphertext,
Some(auth_tag),
)?)
}
pub(crate) fn decrypt_jwe(
jwe: &CompactJwe,
decryption_params: DecryptionParameters,
) -> Result<String> {
let DecryptionParameters::ECDH_ES { local_key_pair } = decryption_params;
let protected_header = jwe
.protected_header()?
.ok_or_else(|| JwCryptoError::IllegalState("protected_header must be present."))?;
if protected_header.alg != Algorithm::ECDH_ES {
return Err(JwCryptoError::IllegalState("alg mismatch."));
}
// Part 1: Reconstruct the secret.
let peer_jwk = protected_header
.epk
.as_ref()
.ok_or_else(|| JwCryptoError::IllegalState("epk not present"))?;
let JwkKeyParameters::EC(ref ec_key_params) = peer_jwk.key_parameters;
let secret = derive_shared_secret(&protected_header, local_key_pair, &ec_key_params)?;
// Part 2: decrypt the payload
if jwe.encrypted_key()?.is_some() {
return Err(JwCryptoError::IllegalState(
"The Encrypted Key must be empty.",
));
}
let encryption_algorithm = match protected_header.enc {
EncryptionAlgorithm::A256GCM => &aead::AES_256_GCM,
};
let auth_tag = jwe
.auth_tag()?
.ok_or_else(|| JwCryptoError::IllegalState("auth_tag must be present."))?;
if auth_tag.len() != encryption_algorithm.tag_len() {
return Err(JwCryptoError::IllegalState(
"The auth tag must be 16 bytes long.",
));
}
let iv = jwe
.iv()?
.ok_or_else(|| JwCryptoError::IllegalState("iv must be present."))?;
let opening_key = aead::OpeningKey::new(&encryption_algorithm, &secret.as_ref())?;
let ciphertext_and_tag: Vec<u8> = [jwe.ciphertext()?, auth_tag].concat();
let nonce = aead::Nonce::try_assume_unique_for_key(&encryption_algorithm, &iv)?;
let aad = aead::Aad::from(jwe.protected_header_raw().as_bytes());
let plaintext = aead::open(&opening_key, nonce, aad, &ciphertext_and_tag)?;
Ok(String::from_utf8(plaintext.to_vec())?)
}
fn derive_shared_secret(
protected_header: &JweHeader,
local_key_pair: EphemeralKeyPair,
peer_key: &ECKeysParameters,
) -> Result<digest::Digest> {
let (private_key, _) = local_key_pair.split();
let peer_public_key_raw_bytes = public_key_from_ec_params(peer_key)?;
let peer_public_key = UnparsedPublicKey::new(&agreement::ECDH_P256, &peer_public_key_raw_bytes);
// Note: We don't support key-wrapping, but if we did `algorithm_id` would be `alg` instead.
let algorithm_id = protected_header.enc.algorithm_id();
let ikm = private_key.agree(&peer_public_key)?;
let apu = protected_header.apu.as_deref().unwrap_or_default();
let apv = protected_header.apv.as_deref().unwrap_or_default();
get_secret_from_ikm(ikm, &apu, &apv, &algorithm_id)
}
fn public_key_from_ec_params(jwk: &ECKeysParameters) -> Result<Vec<u8>> {
let x = base64::decode_config(&jwk.x, base64::URL_SAFE_NO_PAD)?;
let y = base64::decode_config(&jwk.y, base64::URL_SAFE_NO_PAD)?;
if jwk.crv != "P-256" {
return Err(JwCryptoError::PartialImplementation(
"Only P-256 curves are supported.",
));
}
if x.len() != (256 / 8) {
return Err(JwCryptoError::IllegalState("X must be 32 bytes long."));
}
if y.len() != (256 / 8) {
return Err(JwCryptoError::IllegalState("Y must be 32 bytes long."));
}
let mut peer_pub_key: Vec<u8> = vec![0x04];
peer_pub_key.extend_from_slice(&x);
peer_pub_key.extend_from_slice(&y);
Ok(peer_pub_key)
}
fn get_secret_from_ikm(
ikm: InputKeyMaterial,
apu: &str,
apv: &str,
alg: &str,
) -> Result<digest::Digest> {
let secret = ikm.derive(|z| {
let mut buf: Vec<u8> = vec![];
// ConcatKDF (1 iteration since keyLen <= hashLen).
// See rfc7518 section 4.6 for reference.
buf.extend_from_slice(&1u32.to_be_bytes());
buf.extend_from_slice(&z);
// otherinfo
buf.extend_from_slice(&(alg.len() as u32).to_be_bytes());
buf.extend_from_slice(alg.as_bytes());
buf.extend_from_slice(&(apu.len() as u32).to_be_bytes());
buf.extend_from_slice(apu.as_bytes());
buf.extend_from_slice(&(apv.len() as u32).to_be_bytes());
buf.extend_from_slice(apv.as_bytes());
buf.extend_from_slice(&256u32.to_be_bytes());
digest::digest(&digest::SHA256, &buf)
})?;
Ok(secret)
}
pub fn extract_pub_key_jwk(key_pair: &EphemeralKeyPair) -> Result<Jwk> {
let pub_key_bytes = key_pair.public_key().to_bytes()?;
// Uncompressed form (see SECG SEC1 section 2.3.3).
// First byte is 4, then 32 bytes for x, and 32 bytes for y.
assert_eq!(pub_key_bytes.len(), 1 + 32 + 32);
assert_eq!(pub_key_bytes[0], 0x04);
let x = Vec::from(&pub_key_bytes[1..33]);
let x = base64::encode_config(&x, base64::URL_SAFE_NO_PAD);
let y = Vec::from(&pub_key_bytes[33..]);
let y = base64::encode_config(&y, base64::URL_SAFE_NO_PAD);
Ok(Jwk {
kid: None,
key_parameters: JwkKeyParameters::EC(ECKeysParameters {
crv: "P-256".to_owned(),
x,
y,
}),
})
}
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