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use age_core::{
format::{FileKey, Stanza, FILE_KEY_BYTES},
primitives::{aead_decrypt, aead_encrypt, hkdf},
secrecy::{ExposeSecret, SecretString},
};
use bech32::{ToBase32, Variant};
use rand_7::rngs::OsRng;
use std::fmt;
use subtle::ConstantTimeEq;
use x25519_dalek::{EphemeralSecret, PublicKey, StaticSecret};
use zeroize::Zeroize;
use crate::{
error::{DecryptError, EncryptError},
util::{parse_bech32, read::base64_arg},
};
const SECRET_KEY_PREFIX: &str = "age-secret-key-";
const PUBLIC_KEY_PREFIX: &str = "age";
pub(super) const X25519_RECIPIENT_TAG: &str = "X25519";
const X25519_RECIPIENT_KEY_LABEL: &[u8] = b"age-encryption.org/v1/X25519";
pub(super) const EPK_LEN_BYTES: usize = 32;
pub(super) const ENCRYPTED_FILE_KEY_BYTES: usize = FILE_KEY_BYTES + 16;
#[derive(Clone)]
pub struct Identity(StaticSecret);
impl std::str::FromStr for Identity {
type Err = &'static str;
fn from_str(s: &str) -> Result<Self, Self::Err> {
parse_bech32(s)
.ok_or("invalid Bech32 encoding")
.and_then(|(hrp, bytes)| {
if hrp == SECRET_KEY_PREFIX {
TryInto::<[u8; 32]>::try_into(&bytes[..])
.map_err(|_| "incorrect identity length")
.map(StaticSecret::from)
.map(Identity)
} else {
Err("incorrect HRP")
}
})
}
}
impl Identity {
pub fn generate() -> Self {
let mut rng = OsRng;
Identity(StaticSecret::new(&mut rng))
}
pub fn to_string(&self) -> SecretString {
let mut sk_bytes = self.0.to_bytes();
let sk_base32 = sk_bytes.to_base32();
let mut encoded =
bech32::encode(SECRET_KEY_PREFIX, sk_base32, Variant::Bech32).expect("HRP is valid");
let ret = SecretString::new(encoded.to_uppercase());
sk_bytes.zeroize();
encoded.zeroize();
ret
}
pub fn to_public(&self) -> Recipient {
Recipient((&self.0).into())
}
}
impl crate::Identity for Identity {
fn unwrap_stanza(&self, stanza: &Stanza) -> Option<Result<FileKey, DecryptError>> {
if stanza.tag != X25519_RECIPIENT_TAG {
return None;
}
let ephemeral_share = match &stanza.args[..] {
[arg] => match base64_arg(arg, [0; EPK_LEN_BYTES]) {
Some(ephemeral_share) => ephemeral_share,
None => return Some(Err(DecryptError::InvalidHeader)),
},
_ => return Some(Err(DecryptError::InvalidHeader)),
};
if stanza.body.len() != ENCRYPTED_FILE_KEY_BYTES {
return Some(Err(DecryptError::InvalidHeader));
}
let epk: PublicKey = ephemeral_share.into();
let encrypted_file_key: [u8; ENCRYPTED_FILE_KEY_BYTES] = stanza.body[..]
.try_into()
.expect("Length should have been checked above");
let pk: PublicKey = (&self.0).into();
let shared_secret = self.0.diffie_hellman(&epk);
if shared_secret
.as_bytes()
.iter()
.fold(0, |acc, b| acc | b)
.ct_eq(&0)
.into()
{
return Some(Err(DecryptError::InvalidHeader));
}
let mut salt = vec![];
salt.extend_from_slice(epk.as_bytes());
salt.extend_from_slice(pk.as_bytes());
let enc_key = hkdf(&salt, X25519_RECIPIENT_KEY_LABEL, shared_secret.as_bytes());
aead_decrypt(&enc_key, FILE_KEY_BYTES, &encrypted_file_key)
.ok()
.map(|mut pt| {
let file_key: [u8; FILE_KEY_BYTES] = pt[..].try_into().unwrap();
pt.zeroize();
Ok(file_key.into())
})
}
}
#[derive(Clone)]
pub struct Recipient(PublicKey);
impl std::str::FromStr for Recipient {
type Err = &'static str;
fn from_str(s: &str) -> Result<Self, Self::Err> {
parse_bech32(s)
.ok_or("invalid Bech32 encoding")
.and_then(|(hrp, bytes)| {
if hrp == PUBLIC_KEY_PREFIX {
TryInto::<[u8; 32]>::try_into(&bytes[..])
.map_err(|_| "incorrect pubkey length")
.map(PublicKey::from)
.map(Recipient)
} else {
Err("incorrect HRP")
}
})
}
}
impl fmt::Display for Recipient {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
write!(
f,
"{}",
bech32::encode(
PUBLIC_KEY_PREFIX,
self.0.as_bytes().to_base32(),
Variant::Bech32
)
.expect("HRP is valid")
)
}
}
impl crate::Recipient for Recipient {
fn wrap_file_key(&self, file_key: &FileKey) -> Result<Vec<Stanza>, EncryptError> {
let mut rng = OsRng;
let esk = EphemeralSecret::new(&mut rng);
let epk: PublicKey = (&esk).into();
let shared_secret = esk.diffie_hellman(&self.0);
if bool::from(
shared_secret
.as_bytes()
.iter()
.fold(0, |acc, b| acc | b)
.ct_eq(&0),
) {
panic!("Generated the all-zero esk; OS RNG is likely failing!");
}
let mut salt = vec![];
salt.extend_from_slice(epk.as_bytes());
salt.extend_from_slice(self.0.as_bytes());
let enc_key = hkdf(&salt, X25519_RECIPIENT_KEY_LABEL, shared_secret.as_bytes());
let encrypted_file_key = aead_encrypt(&enc_key, file_key.expose_secret());
let encoded_epk = base64::encode_config(epk.as_bytes(), base64::STANDARD_NO_PAD);
Ok(vec![Stanza {
tag: X25519_RECIPIENT_TAG.to_owned(),
args: vec![encoded_epk],
body: encrypted_file_key,
}])
}
}
#[cfg(test)]
pub(crate) mod tests {
use age_core::secrecy::ExposeSecret;
use quickcheck::TestResult;
use quickcheck_macros::quickcheck;
use x25519_dalek::{PublicKey, StaticSecret};
use super::{Identity, Recipient};
use crate::{Identity as _, Recipient as _};
pub(crate) const TEST_SK: &str =
"AGE-SECRET-KEY-1GQ9778VQXMMJVE8SK7J6VT8UJ4HDQAJUVSFCWCM02D8GEWQ72PVQ2Y5J33";
pub(crate) const TEST_PK: &str =
"age1t7rxyev2z3rw82stdlrrepyc39nvn86l5078zqkf5uasdy86jp6svpy7pa";
#[test]
fn pubkey_encoding() {
let pk: Recipient = TEST_PK.parse().unwrap();
assert_eq!(pk.to_string(), TEST_PK);
}
#[test]
fn pubkey_from_secret_key() {
let key = TEST_SK.parse::<Identity>().unwrap();
assert_eq!(key.to_public().to_string(), TEST_PK);
}
#[quickcheck]
fn wrap_and_unwrap(sk_bytes: Vec<u8>) -> TestResult {
if sk_bytes.len() > 32 {
return TestResult::discard();
}
let file_key = [7; 16].into();
let sk = {
let mut tmp = [0; 32];
tmp[..sk_bytes.len()].copy_from_slice(&sk_bytes);
StaticSecret::from(tmp)
};
let stanzas = Recipient(PublicKey::from(&sk))
.wrap_file_key(&file_key)
.unwrap();
let res = Identity(sk).unwrap_stanzas(&stanzas);
match res {
Some(Ok(res)) => TestResult::from_bool(res.expose_secret() == file_key.expose_secret()),
_ => TestResult::from_bool(false),
}
}
}