c2pa 0.91.2

// Copyright 2022 Adobe. All rights reserved.
// This file is licensed to you under the Apache License,
// Version 2.0 (http://www.apache.org/licenses/LICENSE-2.0)
// or the MIT license (http://opensource.org/licenses/MIT),
// at your option.

// Unless required by applicable law or agreed to in writing,
// this software is distributed on an "AS IS" BASIS, WITHOUT
// WARRANTIES OR REPRESENTATIONS OF ANY KIND, either express or
// implied. See the LICENSE-MIT and LICENSE-APACHE files for the
// specific language governing permissions and limitations under
// each license.

use std::io::Read;

use async_generic::async_generic;
use http::header;
use rasn::prelude::*;
use rasn_pkix::Certificate;
use x509_parser::{
    der_parser::{oid, Oid},
    extensions::ParsedExtension,
    prelude::*,
};

use crate::{
    context::{Context, ProgressPhase},
    crypto::base64,
};

const AD_OCSP_OID: Oid<'static> = oid!(1.3.6 .1 .5 .5 .7 .48 .1);
const AUTHORITY_INFO_ACCESS_OID: Oid<'static> = oid!(1.3.6 .1 .5 .5 .7 .1 .1);

// Common types and structures used across all targets
struct OcspRequestData {
    request_str: String,
    url: url::Url,
}

// Common function to extract AIA responders from a certificate
fn extract_aia_responders(cert: &x509_parser::certificate::X509Certificate) -> Option<Vec<String>> {
    let em = cert.extensions_map().ok()?;

    let aia_extension = em.get(&AUTHORITY_INFO_ACCESS_OID)?;

    let ParsedExtension::AuthorityInfoAccess(aia) = aia_extension.parsed_extension() else {
        return None;
    };

    let mut output = Vec::new();

    for ad in &aia.accessdescs {
        if let x509_parser::extensions::GeneralName::URI(uri) = ad.access_location {
            if ad.access_method == AD_OCSP_OID {
                output.push(uri.to_string())
            }
        }
    }
    Some(output)
}

// Common function to build OCSP request data
fn build_ocsp_request(
    subject_der: &[u8],
    issuer_der: &[u8],
    responder_url: &str,
) -> Option<OcspRequestData> {
    let subject: Certificate = rasn::der::decode(subject_der).ok()?;
    let issuer: Certificate = rasn::der::decode(issuer_der).ok()?;

    let issuer_name_raw = rasn::der::encode(&issuer.tbs_certificate.subject).ok()?;
    let issuer_key_raw = &issuer
        .tbs_certificate
        .subject_public_key_info
        .subject_public_key
        .as_raw_slice();

    let issuer_name_hash = OctetString::from(crate::crypto::hash::sha1(&issuer_name_raw));
    let issuer_key_hash = OctetString::from(crate::crypto::hash::sha1(issuer_key_raw));
    let serial_number = subject.tbs_certificate.serial_number;

    // Build request structures
    let sha1_oid = rasn::types::Oid::new(&[1, 3, 14, 3, 2, 26])?;
    let alg = rasn::types::ObjectIdentifier::from(sha1_oid);

    let sha1_ai = rasn_pkix::AlgorithmIdentifier {
        algorithm: alg,
        parameters: Some(Any::new(rasn::der::encode(&()).ok()?)),
        // Many OCSP responders expect this to be NULL not None.
    };

    let req_cert = rasn_ocsp::CertId {
        hash_algorithm: sha1_ai,
        issuer_name_hash,
        issuer_key_hash,
        serial_number,
    };

    let ocsp_req = rasn_ocsp::Request {
        req_cert,
        single_request_extensions: None,
    };

    let request_list = vec![ocsp_req];

    let tbs_request = rasn_ocsp::TbsRequest {
        version: rasn_ocsp::Version::from(0u8),
        requestor_name: None,
        request_list,
        request_extensions: None,
    };

    let ocsp_request = rasn_ocsp::OcspRequest {
        tbs_request,
        optional_signature: None,
    };

    let request_der = rasn::der::encode(&ocsp_request).ok()?;
    let request_str = base64::encode(&request_der);
    let url = url::Url::parse(responder_url).ok()?;

    Some(OcspRequestData { request_str, url })
}

// Build OCSP requests for the certificate at `subject_index`, read from its own
// AIA responder(s) with `certs[subject_index + 1]` as the issuer. This lets each
// certificate in the chain (the leaf and each issuing CA) be queried, not just
// the leaf.
fn process_ocsp_responders(
    certs: &[Vec<u8>],
    subject_index: usize,
) -> Option<Vec<OcspRequestData>> {
    let subject_der = certs.get(subject_index)?;
    let issuer_der = certs.get(subject_index + 1)?;

    let (_rem, cert) = X509Certificate::from_der(subject_der).ok()?;

    let requests: Vec<_> = extract_aia_responders(&cert)
        .into_iter()
        .flat_map(|responders| {
            responders
                .into_iter()
                .filter_map(|responder| build_ocsp_request(subject_der, issuer_der, &responder))
        })
        .collect();

    if requests.is_empty() {
        None
    } else {
        Some(requests)
    }
}

/// Retrieve an OCSP response for the certificate at `subject_index` if available.
///
/// Checks for an OCSP responder in that certificate's AIA extension. If found,
/// it will attempt to retrieve the raw DER-encoded OCSP response.
#[async_generic]
pub(crate) fn fetch_ocsp_response(
    certs: &[Vec<u8>],
    subject_index: usize,
    context: &Context,
) -> Option<Vec<u8>> {
    let requests = process_ocsp_responders(certs, subject_index)?;
    let requests_len = requests.len() as u32;
    for (step, request_data) in (1..).zip(requests) {
        context
            .check_progress(ProgressPhase::FetchingOCSP, step, requests_len)
            .ok()?;
        let req_url = request_data.url.join(&request_data.request_str).ok()?;

        let mut request = http::Request::get(req_url.to_string());
        if let Some(host) = req_url.host() {
            // for responders that don't support http 1.0
            request = request.header(header::HOST, host.to_string());
        }

        let request = request.body(Vec::new()).ok()?;
        let response = if _sync {
            context.resolver().http_resolve(request).ok()?
        } else {
            context
                .resolver_async()
                .http_resolve_async(request)
                .await
                .ok()?
        };

        if response.status() == 200 {
            let len = response
                .headers()
                .get(header::CONTENT_LENGTH)
                .and_then(|content_length| content_length.to_str().ok())
                .and_then(|content_length| content_length.parse().ok())
                .unwrap_or(10000);

            let mut ocsp_rsp: Vec<u8> = Vec::with_capacity(len);

            response
                .into_body()
                .take(1000000)
                .read_to_end(&mut ocsp_rsp)
                .ok()?;

            return Some(ocsp_rsp);
        }
    }
    None
}

#[cfg(test)]
mod tests {
    #![allow(clippy::unwrap_used)]

    use super::process_ocsp_responders;
    use crate::crypto::cert_chain_pem_to_der;

    // [leaf(AIA=leaf-ocsp.test), issuing CA(AIA=ca-ocsp.test), root].
    fn ca_chain() -> Vec<Vec<u8>> {
        let pem = include_bytes!("../../../tests/fixtures/crypto/ocsp/ocsp_ca_chain.pem");
        cert_chain_pem_to_der(pem).unwrap()
    }

    fn responder_hosts(certs: &[Vec<u8>], subject_index: usize) -> Vec<String> {
        process_ocsp_responders(certs, subject_index)
            .unwrap()
            .iter()
            .filter_map(|r| r.url.host_str().map(|h| h.to_string()))
            .collect()
    }

    #[test]
    fn each_cert_is_queried_against_its_own_responder() {
        let certs = ca_chain();

        // The leaf is queried against its own responder...
        let leaf_hosts = responder_hosts(&certs, 0);
        assert!(leaf_hosts.iter().any(|h| h == "leaf-ocsp.test"));
        assert!(!leaf_hosts.iter().any(|h| h == "ca-ocsp.test"));

        // ...and the issuing CA against its own responder (the fix: previously
        // the CA was never contacted, so a revoked CA went undetected).
        let ca_hosts = responder_hosts(&certs, 1);
        assert!(ca_hosts.iter().any(|h| h == "ca-ocsp.test"));
    }
}