1 files changed, 235 insertions, 0 deletions
diff --git a/third_party/rust/cose/src/decoder.rs b/third_party/rust/cose/src/decoder.rs
new file mode 100644
index 0000000000..90463d5dd2
--- /dev/null
+++ b/third_party/rust/cose/src/decoder.rs
@@ -0,0 +1,235 @@
+//! Parse and decode COSE signatures.
+
+use cbor::CborType;
+use cbor::decoder::decode;
+use {CoseError, SignatureAlgorithm};
+use util::get_sig_struct_bytes;
+use std::collections::BTreeMap;
+
+pub const COSE_SIGN_TAG: u64 = 98;
+
+/// The result of `decode_signature` holding a decoded COSE signature.
+#[derive(Debug)]
+pub struct CoseSignature {
+    pub signature_type: SignatureAlgorithm,
+    pub signature: Vec<u8>,
+    pub signer_cert: Vec<u8>,
+    pub certs: Vec<Vec<u8>>,
+    pub to_verify: Vec<u8>,
+}
+
+pub const COSE_TYPE_ES256: i64 = -7;
+pub const COSE_TYPE_ES384: i64 = -35;
+pub const COSE_TYPE_ES512: i64 = -36;
+pub const COSE_TYPE_PS256: i64 = -37;
+
+pub const COSE_HEADER_ALG: u64 = 1;
+pub const COSE_HEADER_KID: u64 = 4;
+
+macro_rules! unpack {
+   ($to:tt, $var:ident) => (
+        match *$var {
+            CborType::$to(ref cbor_object) => {
+                cbor_object
+            }
+            _ => return Err(CoseError::UnexpectedType),
+        };
+    )
+}
+
+fn get_map_value(
+    map: &BTreeMap<CborType, CborType>,
+    key: &CborType,
+) -> Result<CborType, CoseError> {
+    match map.get(key) {
+        Some(x) => Ok(x.clone()),
+        _ => Err(CoseError::MissingHeader),
+    }
+}
+
+/// Ensure that the referenced `CborType` is an empty map.
+fn ensure_empty_map(map: &CborType) -> Result<(), CoseError> {
+    let unpacked = unpack!(Map, map);
+    if !unpacked.is_empty() {
+        return Err(CoseError::MalformedInput);
+    }
+    Ok(())
+}
+
+// This syntax is a little unintuitive. Taken together, the two previous definitions essentially
+// mean:
+//
+// COSE_Sign = [
+//     protected : empty_or_serialized_map,
+//     unprotected : header_map
+//     payload : bstr / nil,
+//     signatures : [+ COSE_Signature]
+// ]
+//
+// (COSE_Sign is an array. The first element is an empty or serialized map (in our case, it is
+// never expected to be empty). The second element is a map (it is expected to be empty. The third
+// element is a bstr or nil (it is expected to be nil). The fourth element is an array of
+// COSE_Signature.)
+//
+// COSE_Signature =  [
+//     Headers,
+//     signature : bstr
+// ]
+//
+// but again, unpacking this:
+//
+// COSE_Signature =  [
+//     protected : empty_or_serialized_map,
+//     unprotected : header_map
+//     signature : bstr
+// ]
+fn decode_signature_struct(
+    cose_signature: &CborType,
+    payload: &[u8],
+    protected_body_head: &CborType,
+) -> Result<CoseSignature, CoseError> {
+    let cose_signature = unpack!(Array, cose_signature);
+    if cose_signature.len() != 3 {
+        return Err(CoseError::MalformedInput);
+    }
+    let protected_signature_header_serialized = &cose_signature[0];
+    let protected_signature_header_bytes = unpack!(Bytes, protected_signature_header_serialized);
+
+    // Parse the protected signature header.
+    let protected_signature_header = &match decode(protected_signature_header_bytes) {
+        Err(_) => return Err(CoseError::DecodingFailure),
+        Ok(value) => value,
+    };
+    let protected_signature_header = unpack!(Map, protected_signature_header);
+    if protected_signature_header.len() != 2 {
+        return Err(CoseError::MalformedInput);
+    }
+    let signature_algorithm = get_map_value(
+        protected_signature_header,
+        &CborType::Integer(COSE_HEADER_ALG),
+    )?;
+    let signature_algorithm = match signature_algorithm {
+        CborType::SignedInteger(val) => {
+            match val {
+                COSE_TYPE_ES256 => SignatureAlgorithm::ES256,
+                COSE_TYPE_ES384 => SignatureAlgorithm::ES384,
+                COSE_TYPE_ES512 => SignatureAlgorithm::ES512,
+                COSE_TYPE_PS256 => SignatureAlgorithm::PS256,
+                _ => return Err(CoseError::UnexpectedHeaderValue),
+            }
+        }
+        _ => return Err(CoseError::UnexpectedType),
+    };
+
+    let ee_cert = &get_map_value(
+        protected_signature_header,
+        &CborType::Integer(COSE_HEADER_KID),
+    )?;
+    let ee_cert = unpack!(Bytes, ee_cert).clone();
+
+    // The unprotected header section is expected to be an empty map.
+    ensure_empty_map(&cose_signature[1])?;
+
+    // Build signature structure to verify.
+    let signature_bytes = &cose_signature[2];
+    let signature_bytes = unpack!(Bytes, signature_bytes).clone();
+    let sig_structure_bytes = get_sig_struct_bytes(
+        protected_body_head.clone(),
+        protected_signature_header_serialized.clone(),
+        payload,
+    );
+
+    // Read intermediate certificates from protected_body_head.
+    // Any tampering of the protected header during transport will be detected
+    // because it is input to the signature verification.
+    // Note that a protected header has to be present and hold a kid with an
+    // empty list of intermediate certificates.
+    let protected_body_head_bytes = unpack!(Bytes, protected_body_head);
+    let protected_body_head_map = &match decode(protected_body_head_bytes) {
+        Ok(value) => value,
+        Err(_) => return Err(CoseError::DecodingFailure),
+    };
+    let protected_body_head_map = unpack!(Map, protected_body_head_map);
+    if protected_body_head_map.len() != 1 {
+        return Err(CoseError::MalformedInput);
+    }
+    let intermediate_certs_array =
+        &get_map_value(protected_body_head_map, &CborType::Integer(COSE_HEADER_KID))?;
+    let intermediate_certs = unpack!(Array, intermediate_certs_array);
+    let mut certs: Vec<Vec<u8>> = Vec::new();
+    for cert in intermediate_certs {
+        let cert = unpack!(Bytes, cert);
+        certs.push(cert.clone());
+    }
+
+    Ok(CoseSignature {
+        signature_type: signature_algorithm,
+        signature: signature_bytes,
+        signer_cert: ee_cert,
+        certs: certs,
+        to_verify: sig_structure_bytes,
+    })
+}
+
+/// Decode COSE signature bytes and return a vector of `CoseSignature`.
+///
+///```rust,ignore
+/// COSE_Sign = [
+///     Headers,
+///     payload : bstr / nil,
+///     signatures : [+ COSE_Signature]
+/// ]
+///
+/// Headers = (
+///     protected : empty_or_serialized_map,
+///     unprotected : header_map
+/// )
+///```
+pub fn decode_signature(bytes: &[u8], payload: &[u8]) -> Result<Vec<CoseSignature>, CoseError> {
+    // This has to be a COSE_Sign object, which is a tagged array.
+    let tagged_cose_sign = match decode(bytes) {
+        Err(_) => return Err(CoseError::DecodingFailure),
+        Ok(value) => value,
+    };
+    let cose_sign_array = match tagged_cose_sign {
+        CborType::Tag(tag, cose_sign) => {
+            if tag != COSE_SIGN_TAG {
+                return Err(CoseError::UnexpectedTag);
+            }
+            match *cose_sign {
+                CborType::Array(values) => values,
+                _ => return Err(CoseError::UnexpectedType),
+            }
+        }
+        _ => return Err(CoseError::UnexpectedType),
+    };
+    if cose_sign_array.len() != 4 {
+        return Err(CoseError::MalformedInput);
+    }
+
+    // The unprotected header section is expected to be an empty map.
+    ensure_empty_map(&cose_sign_array[1])?;
+
+    // The payload is expected to be Null (i.e. this is a detached signature).
+    match cose_sign_array[2] {
+        CborType::Null => {}
+        _ => return Err(CoseError::UnexpectedType),
+    };
+
+    let signatures = &cose_sign_array[3];
+    let signatures = unpack!(Array, signatures);
+
+    // Decode COSE_Signatures.
+    // There has to be at least one signature to make this a valid COSE signature.
+    if signatures.len() < 1 {
+        return Err(CoseError::MalformedInput);
+    }
+    let mut result = Vec::new();
+    for cose_signature in signatures {
+        // cose_sign_array[0] holds the protected body header.
+        let signature = decode_signature_struct(cose_signature, payload, &cose_sign_array[0])?;
+        result.push(signature);
+    }
+
+    Ok(result)
+}