implement hmac extension

src/extensions/hmac.rs

@@ -0,0 +1,200 @@
+use crate::cbor;
+use crate::{FidoCredential, FidoDevice, FidoErrorKind, FidoResult};
+use cbor_codec::value::{Bytes, Int, Key, Text, Value};
+use cbor_codec::Encoder;
+use cbor_codec::{Config, GenericDecoder};
+use rust_crypto::buffer::{RefReadBuffer, RefWriteBuffer};
+use rust_crypto::digest::Digest;
+use rust_crypto::hmac::Hmac;
+use rust_crypto::mac::Mac;
+use rust_crypto::sha2::Sha256;
+use std::collections::BTreeMap;
+use std::io::Cursor;
+
+#[derive(Debug, Clone)]
+pub struct FidoHmacCredential {
+    pub id: Vec<u8>,
+    pub rp_id: String,
+}
+
+impl From<FidoCredential> for FidoHmacCredential {
+    fn from(cred: FidoCredential) -> Self {
+        FidoHmacCredential {
+            id: cred.id,
+            rp_id: cred.rp_id,
+        }
+    }
+}
+
+pub trait HmacExtension {
+    fn extension_name() -> &'static str {
+        "hmac-secret"
+    }
+
+    fn get_dict(&mut self, salt: &[u8; 32], salt2: Option<&[u8; 32]>) -> FidoResult<Value> {
+        let mut map = BTreeMap::new();
+        map.insert(
+            Key::Text(Text::Text(Self::extension_name().to_owned())),
+            self.get_data(salt, salt2)?,
+        );
+        Ok(Value::Map(map))
+    }
+
+    fn get_data(&mut self, salt: &[u8; 32], salt2: Option<&[u8; 32]>) -> FidoResult<Value>;
+
+    fn make_hmac_credential(&mut self) -> FidoResult<FidoHmacCredential>;
+
+    fn get_hmac_assertion(
+        &mut self,
+        credential: &FidoHmacCredential,
+        salt: &[u8; 32],
+        salt2: Option<&[u8; 32]>,
+    ) -> FidoResult<([u8; 32], Option<[u8; 32]>)>;
+
+    fn hmac_challange(
+        &mut self,
+        credential: &FidoHmacCredential,
+        input: &[u8],
+    ) -> FidoResult<[u8; 32]> {
+        let mut salt = [0u8; 32];
+        let mut digest = Sha256::new();
+        digest.input(input);
+        digest.result(&mut salt);
+        self.get_hmac_assertion(credential, &salt, None)
+            .map(|secret| secret.0)
+    }
+}
+
+impl HmacExtension for FidoDevice {
+    fn get_data(&mut self, salt: &[u8; 32], salt2: Option<&[u8; 32]>) -> FidoResult<Value> {
+        let shared_secret = self.shared_secret.as_ref().unwrap();
+        let mut encryptor = shared_secret.encryptor();
+        let mut salt_enc = [0u8; 64];
+        let mut output = RefWriteBuffer::new(&mut salt_enc);
+        let mut encrypt = || {
+            encryptor.encrypt(&mut RefReadBuffer::new(salt), &mut output, salt2.is_none())?;
+            if let Some(salt2) = salt2 {
+                encryptor
+                    .encrypt(&mut RefReadBuffer::new(salt2), &mut output, true)
+                    .map(|_| ())
+            } else {
+                Ok(())
+            }
+        };
+        encrypt().map_err(|_| FidoErrorKind::Io)?;
+
+        let key_agreement = || {
+            let mut cur = Cursor::new(Vec::new());
+            let mut encoder = Encoder::new(&mut cur);
+            shared_secret.public_key.encode(&mut encoder).unwrap();
+            cur.set_position(0);
+            let mut dec = GenericDecoder::new(Config::default(), cur);
+            dec.value()
+        };
+
+        let mut map = BTreeMap::new();
+        map.insert(
+            Key::Int(Int::from_i64(0x01)),
+            key_agreement().map_err(|_| FidoErrorKind::Io)?,
+        );
+        map.insert(
+            Key::Int(Int::from_i64(0x02)),
+            Value::Bytes(Bytes::Bytes(
+                salt_enc[0..((salt2.is_some() as usize + 1) * 32)].to_vec(),
+            )),
+        );
+
+        let mut salt_hmac = Hmac::new(Sha256::new(), &shared_secret.shared_secret);
+        salt_hmac.input(&salt_enc[0..((salt2.is_some() as usize + 1) * 32)]);
+
+        let mut authed_salt_enc = [0u8; 32];
+        authed_salt_enc.copy_from_slice(salt_hmac.result().code());
+
+        map.insert(
+            Key::Int(Int::from_i64(0x03)),
+            Value::Bytes(Bytes::Bytes(authed_salt_enc[0..16].to_vec())),
+        );
+
+        Ok(Value::Map(map))
+    }
+
+    fn make_hmac_credential(&mut self) -> FidoResult<FidoHmacCredential> {
+        self.make_credential("hmac", &[0u8], "commandline", &[0u8; 32])
+            .map(|cred| cred.into())
+    }
+
+    fn get_hmac_assertion(
+        &mut self,
+        credential: &FidoHmacCredential,
+        salt: &[u8; 32],
+        salt2: Option<&[u8; 32]>,
+    ) -> FidoResult<([u8; 32], Option<[u8; 32]>)> {
+        let client_data_hash = [0u8; 32];
+        while self.shared_secret.is_none() {
+            self.init_shared_secret()?;
+        }
+        if self.needs_pin && self.pin_token.is_none() {
+            Err(FidoErrorKind::PinRequired)?
+        }
+
+        if client_data_hash.len() != 32 {
+            Err(FidoErrorKind::CborEncode)?
+        }
+        let pin_auth = self
+            .pin_token
+            .as_ref()
+            .map(|token| token.auth(&client_data_hash));
+        let ext_data: Value = self.get_data(salt, salt2)?;
+        let allow_list = [cbor::PublicKeyCredentialDescriptor {
+            cred_type: String::from("public-key"),
+            id: credential.id.clone(),
+        }];
+        let request = cbor::GetAssertionRequest {
+            rp_id: &credential.rp_id,
+            client_data_hash: &client_data_hash,
+            allow_list: &allow_list,
+            extensions: &[(<Self as HmacExtension>::extension_name(), &ext_data)],
+            options: Some(cbor::AuthenticatorOptions {
+                rk: false,
+                uv: true,
+            }),
+            pin_auth,
+            pin_protocol: pin_auth.and(Some(0x01)),
+        };
+        let response = match self.cbor(cbor::Request::GetAssertion(request))? {
+            cbor::Response::GetAssertion(resp) => resp,
+            _ => Err(FidoErrorKind::CborDecode)?,
+        };
+        let shared_secret = self.shared_secret.as_ref().unwrap();
+        let mut decryptor = shared_secret.decryptor();
+        let mut hmac_secret_combined = [0u8; 64];
+        let _output = RefWriteBuffer::new(&mut hmac_secret_combined);
+        let hmac_secret_enc = match response
+            .auth_data
+            .extensions
+            .get(<Self as HmacExtension>::extension_name())
+            .ok_or(FidoErrorKind::CborDecode)?
+        {
+            Value::Bytes(hmac_ciphered) => Ok(match hmac_ciphered {
+                Bytes::Bytes(hmac_ciphered) => hmac_ciphered.to_vec(),
+                Bytes::Chunks(hmac_ciphered) => hmac_ciphered.iter().fold(Vec::new(), |s, i| {
+                    let mut s = s;
+                    s.extend_from_slice(&i);
+                    s
+                }),
+            }),
+            _ => Err(FidoErrorKind::CborDecode),
+        }?;
+        let mut hmac_secret = ([0u8; 32], [0u8; 32]);
+        decryptor
+            .decrypt(
+                &mut RefReadBuffer::new(&hmac_secret_enc),
+                &mut RefWriteBuffer::new(unsafe {
+                    std::mem::transmute::<_, &mut [u8; 64]>(&mut hmac_secret)
+                }),
+                true,
+            )
+            .expect("failed to decrypt secret");
+        Ok((hmac_secret.0, salt2.map(|_| hmac_secret.1)))
+    }
+}

src/extensions/mod.rs

@@ -0,0 +1 @@
+pub mod hmac;