Log the signing algorithms of the certificate chain.

src/main/kotlin/Verifier.kt

@@ -83,22 +83,22 @@ interface VerifyRequestLog {
    *
    * @param inputChain The certificate chain which is being verified.
    */
-  fun logInputChain(inputChain: List<ByteString>)
+  fun logInputChain(inputChain: List<ByteString>) {}
 
   /**
    * Logs the result of the verification. Called for each call to [verify].
    *
    * @param result The result of the verification.
    */
-  fun logResult(result: VerificationResult)
+  fun logResult(result: VerificationResult) {}
 
   /**
    * Logs the key description of the leaf certificate. Called if [verify] reaches the point where
    * the key description is parsed.
    *
    * @param keyDescription The key description of the leaf certificate.
    */
-  fun logKeyDescription(keyDescription: KeyDescription)
+  fun logKeyDescription(keyDescription: KeyDescription) {}
 
   /**
    * Logs the provisioning info map extension of the attestation certificate. Called if [verify]
@@ -107,7 +107,7 @@ interface VerifyRequestLog {
    *
    * @param provisioningInfoMap The provisioning info map extension of the leaf certificate.
    */
-  fun logProvisioningInfoMap(provisioningInfoMap: ProvisioningInfoMap)
+  fun logProvisioningInfoMap(provisioningInfoMap: ProvisioningInfoMap) {}
 
   /**
    * Logs the serial numbers of the intermediate certificates in the certificate chain. Called if
@@ -116,17 +116,25 @@ interface VerifyRequestLog {
    * @param certSerialNumbers The serial numbers of the intermediate certificates in the certificate
    *   chain.
    */
-  fun logCertSerialNumbers(certSerialNumbers: List<String>)
+  fun logCertSerialNumbers(certSerialNumbers: List<String>) {}
+
+  /**
+   * Logs the certificate signing algorithms of the intermediate certificates in the certificate
+   * chain. Called if [verify] reaches the point where the certificate chain is validated.
+   *
+   * @param certSigningAlgorithms The certificate signing algorithms in the chain.
+   */
+  fun logCertSigningAlgorithms(certSigningAlgorithms: Set<String>) {}
 
   /**
    * Logs an info level message. May be called throughout the verification process.
    *
    * @param infoMessage The info level message to log.
    */
-  fun logInfoMessage(infoMessage: String)
+  fun logInfoMessage(infoMessage: String) {}
 
   /* Flushes any buffered logs. Called just before [verify] returns. */
-  fun flush()
+  fun flush() {}
 }
 
 /**
@@ -267,6 +275,8 @@ constructor(
         return VerificationResult.PathValidationFailure(e)
       }
 
+    log?.logCertSigningAlgorithms(certPath.signingAlgorithms())
+
     val keyDescription =
       try {
         checkNotNull(

src/main/kotlin/provider/KeyAttestationCertPath.kt

@@ -19,9 +19,14 @@ package com.android.keyattestation.verifier.provider
 import com.android.keyattestation.verifier.SecurityLevel
 import com.android.keyattestation.verifier.asX509Certificate
 import com.google.protobuf.ByteString
+import java.security.PublicKey
 import java.security.cert.CertPath
 import java.security.cert.CertificateException
 import java.security.cert.X509Certificate
+import java.security.interfaces.DSAPublicKey
+import java.security.interfaces.ECPublicKey
+import java.security.interfaces.RSAPublicKey
+import javax.crypto.interfaces.DHPublicKey
 import javax.security.auth.x500.X500Principal
 
 /**
@@ -72,6 +77,18 @@ class KeyAttestationCertPath(certs: List<X509Certificate>) : CertPath("X.509") {
    */
   fun serialNumbers() = certificatesWithAnchor.map { it.serialNumber.toString(16) }
 
+  /**
+   * Returns the signing algorithms of the certificates in the certificate chain.
+   *
+   * The format is "algNameKeySizeN".
+   *
+   * @return the signing algorithms of the certificates in the certificate chain.
+   */
+  fun signingAlgorithms() =
+    certificatesWithAnchor
+      .zipWithNext { cert, issuer -> "${cert.sigAlgName}KeySize${issuer.publicKey.keySize()}" }
+      .toSet()
+
   fun provisioningMethod() =
     when {
       isFactoryProvisioned() -> ProvisioningMethod.FACTORY_PROVISIONED
@@ -152,6 +169,15 @@ private fun parseDN(dn: String): Map<String, String> {
   return attributes
 }
 
+private fun PublicKey.keySize() =
+  when (this) {
+    is RSAPublicKey -> this.modulus.bitLength().toString()
+    is ECPublicKey -> this.params.curve.field.fieldSize.toString()
+    is DSAPublicKey -> this.y.bitLength().toString()
+    is DHPublicKey -> this.y.bitLength().toString()
+    else -> "unknown"
+  }
+
 private fun String?.toSecurityLevel() =
   when (this) {
     "TEE" -> SecurityLevel.TRUSTED_ENVIRONMENT

src/main/kotlin/testing/FakeLogHook.kt

@@ -51,6 +51,7 @@ class FakeVerifyRequestLog : VerifyRequestLog {
   var provisioningInfoMap: ProvisioningInfoMap? = null
   var certSerialNumbers = mutableListOf<String>()
   var infoMessages = mutableListOf<String>()
+  var certSigningAlgorithms = mutableSetOf<String>()
 
   override fun logInputChain(inputChain: List<ByteString>) {
     this.inputChain.addAll(inputChain)
@@ -72,6 +73,10 @@ class FakeVerifyRequestLog : VerifyRequestLog {
     this.certSerialNumbers.addAll(certSerialNumbers)
   }
 
+  override fun logCertSigningAlgorithms(certSigningAlgorithms: Set<String>) {
+    this.certSigningAlgorithms.addAll(certSigningAlgorithms)
+  }
+
   override fun logInfoMessage(infoMessage: String) {
     this.infoMessages.add(infoMessage)
   }

src/test/kotlin/provider/KeyAttestationCertPathTest.kt

@@ -101,6 +101,16 @@ class KeyAttestationCertPathTest {
       .inOrder()
   }
 
+  @Test
+  fun signingAlgorithms_returnsExpectedSigningAlgorithms() {
+    assertThat(readCertPath("blueline/sdk28/TEE_EC_NONE.pem").signingAlgorithms())
+      .containsExactly(
+        "SHA256withECDSAKeySize256",
+        "SHA256withECDSAKeySize384",
+        "SHA256withRSAKeySize4096",
+      )
+  }
+
   @Test
   fun provisioningMethod_returnsExpectedType(@TestParameter testCase: ProvisioningMethodTestCase) {
     val certPath = readCertPath("${testCase.path}.pem")