Add cosign verify-bundle example

Cargo.toml

@@ -73,6 +73,10 @@ serial_test = "0.10.0"
 name = "verify"
 path = "examples/cosign/verify/main.rs"
 
+[[example]]
+name = "verify-bundle"
+path = "examples/cosign/verify-bundle/main.rs"
+
 [[example]]
 name = "sign"
 path = "examples/cosign/sign/main.rs"

examples/cosign/verify-bundle/.gitignore

@@ -0,0 +1,2 @@
+artifact.bundle
+artifact.txt

examples/cosign/verify-bundle/README.md

@@ -0,0 +1,20 @@
+This example shows how to verify a blob, using a bundle that was created by the
+`cosign sign-blob` command.
+
+### Create the artifact to be signed.
+```console
+echo something > artifact.txt
+```
+
+### Sign the artifact.txt file using cosign
+```
+COSIGN_EXPERIMENTAL=1 cosign sign-blob --bundle=artifact.bundle artifact.txt
+```
+
+### Verify using sigstore-rs:
+```console
+cargo run --example verify-bundle -- \
+    --rekor-pub-key ~/.sigstore/root/targets/rekor.pub \
+    --bundle artifact.bundle \
+    artifact.txt
+```

examples/cosign/verify-bundle/main.rs

@@ -0,0 +1,68 @@
+//
+// Copyright 2021 The Sigstore Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use clap::Parser;
+use sigstore::cosign::bundle::SignedArtifactBundle;
+use sigstore::crypto::{CosignVerificationKey, SigningScheme};
+use std::fs;
+use tracing_subscriber::prelude::*;
+use tracing_subscriber::{fmt, EnvFilter};
+
+#[derive(Parser, Debug)]
+#[clap(author, version, about, long_about = None)]
+struct Cli {
+    /// Path to bundle file
+    #[clap(short, long)]
+    bundle: String,
+
+    /// Path to artifact to be verified
+    blob: String,
+
+    /// File containing Rekor's public key (e.g.: ~/.sigstore/root/targets/rekor.pub)
+    #[clap(long, required(false))]
+    rekor_pub_key: String,
+
+    /// Enable verbose mode
+    #[clap(short, long)]
+    verbose: bool,
+}
+
+#[tokio::main]
+pub async fn main() {
+    let cli = Cli::parse();
+
+    // setup logging
+    let level_filter = if cli.verbose { "debug" } else { "info" };
+    let filter_layer = EnvFilter::new(level_filter);
+    tracing_subscriber::registry()
+        .with(filter_layer)
+        .with(fmt::layer().with_writer(std::io::stderr))
+        .init();
+
+    let rekor_pub_pem =
+        fs::read_to_string(&cli.rekor_pub_key).expect("error reading rekor's public key");
+    let rekor_pub_key =
+        CosignVerificationKey::from_pem(rekor_pub_pem.as_bytes(), &SigningScheme::default())
+            .expect("Cannot create Rekor verification key");
+    let bundle_json = fs::read_to_string(&cli.bundle).expect("error reading bundle json file");
+    let blob = fs::read(&cli.blob.as_str()).expect("error reading blob file");
+
+    let bundle = SignedArtifactBundle::new_verified(&bundle_json, &rekor_pub_key).unwrap();
+    if bundle.verify_blob(&blob).is_ok() {
+        println!("Verification succeeded");
+    } else {
+        eprintln!("Verification failed");
+    }
+}

examples/cosign/verify-bundle/run.sh

@@ -0,0 +1,17 @@
+BLOB="artifact.txt"
+BUNDLE="artifact.bundle"
+
+echo -e "\nGenerate the blob to be signed"
+echo something > $BLOB
+
+echo -e "\nSign the artifact.txt file using sign-blob"
+COSIGN_EXPERIMENTAL=1 cosign sign-blob --bundle=$BUNDLE $BLOB
+
+echo -e "\nVerify using cosign. TODO: remove this later"
+cosign verify-blob --bundle=$BUNDLE $BLOB
+
+echo -e "\nRun examples/cosign/verify-bundle"
+cargo run --example verify-bundle -- \
+    --rekor-pub-key ~/.sigstore/root/targets/rekor.pub \
+    --bundle $BUNDLE \
+    $BLOB

src/cosign/bundle.rs

@@ -13,9 +13,11 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+use base64::{engine::general_purpose::STANDARD as BASE64_STD_ENGINE, Engine as _};
 use olpc_cjson::CanonicalFormatter;
 use serde::{Deserialize, Serialize};
 use std::cmp::PartialEq;
+use std::convert::TryFrom;
 
 use crate::crypto::{CosignVerificationKey, Signature};
 use crate::errors::{Result, SigstoreError};
@@ -43,13 +45,26 @@ impl SignedArtifactBundle {
     ///
     /// **Note well:** The bundle will be returned only if it can be verified
     /// using the supplied `rekor_pub_key` public key.
-    #[allow(dead_code)]
-    pub(crate) fn new_verified(raw: &str, rekor_pub_key: &CosignVerificationKey) -> Result<Self> {
+    pub fn new_verified(raw: &str, rekor_pub_key: &CosignVerificationKey) -> Result<Self> {
         let bundle: SignedArtifactBundle = serde_json::from_str(raw).map_err(|e| {
             SigstoreError::UnexpectedError(format!("Cannot parse bundle |{}|: {:?}", raw, e))
         })?;
         Bundle::verify_bundle(&bundle.rekor_bundle, rekor_pub_key).map(|_| bundle)
     }
+
+    /// Verifies the passed-in blob against the signature in this
+    /// SignedArtifactBundle.
+    pub fn verify_blob(&self, blob: &[u8]) -> Result<()> {
+        let cert = BASE64_STD_ENGINE.decode(&self.cert)?;
+        let (_, pem) = x509_parser::pem::parse_x509_pem(&cert)?;
+        let (_, cert) = x509_parser::parse_x509_certificate(&pem.contents)?;
+        let subject_public_key = cert.public_key();
+        let ver_key =
+            CosignVerificationKey::try_from(subject_public_key).expect("conversion failed");
+        let signature = Signature::Base64Encoded(self.base64_signature.as_bytes());
+        ver_key.verify_signature(signature, blob)?;
+        Ok(())
+    }
 }
 
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq)]

src/cosign/mod.rs

@@ -44,7 +44,7 @@ use tracing::warn;
 use crate::errors::{Result, SigstoreApplicationConstraintsError, SigstoreVerifyConstraintsError};
 use crate::registry::{Auth, PushResponse};
 
-mod bundle;
+pub mod bundle;
 pub(crate) mod constants;
 pub mod signature_layers;
 pub use signature_layers::SignatureLayer;