Validate PublicKeyAlgorithmPolicy when generating keys

pgpainless-core/src/main/kotlin/org/pgpainless/key/generation/OpenPgpKeyBuilder.kt

@@ -42,6 +42,14 @@ open class OpenPgpKeyBuilder(
         flags: List<KeyFlag>? = listOf(KeyFlag.CERTIFY_OTHER)
     ): V4OpenPgpKeyBuilder = V4OpenPgpKeyBuilder(keyType, flags, policy, referenceTime, preferences)
 
+    internal fun verifyAlgorithmComplianceWithPolicy(keyType: KeyType, policy: Policy) {
+        val algorithm = keyType.algorithm
+        val bitStrength = keyType.bitStrength
+        require(policy.publicKeyAlgorithmPolicy.isAcceptable(algorithm, bitStrength)) {
+            "Public key algorithm policy violation: $algorithm with bit strength $bitStrength is not acceptable."
+        }
+    }
+
     /**
      * Builder for version 4 OpenPGP keys.
      *
@@ -60,6 +68,10 @@ open class OpenPgpKeyBuilder(
         preferences: AlgorithmSuite
     ) : OpenPgpKeyBuilder(policy, referenceTime, preferences) {
 
+        init {
+            verifyAlgorithmComplianceWithPolicy(primaryKeyType, policy)
+        }
+
         private val primaryKey =
             BaseOpenPgpKeyBuilder.BaseV4PrimaryKeyBuilder(primaryKeyType, referenceTime, policy)
         private val subkeys = mutableListOf<BaseOpenPgpKeyBuilder.BaseV4SubkeyBuilder>()
@@ -140,6 +152,7 @@ open class OpenPgpKeyBuilder(
             subkeyBuilder: BaseOpenPgpKeyBuilder.BaseV4SubkeyBuilder,
             subpacketsCallback: SelfSignatureSubpackets.Callback = SelfSignatureSubpackets.nop()
         ) = apply {
+            verifyAlgorithmComplianceWithPolicy(subkeyBuilder.type, policy)
             subkeys.add(subkeyBuilder.bindingSignature(subpacketsCallback = subpacketsCallback))
         }
 

pgpainless-core/src/test/kotlin/org/pgpainless/key/generation/OpenPgpKeyBuilderTest.kt

@@ -3,10 +3,13 @@ package org.pgpainless.key.generation
 import org.bouncycastle.bcpg.attr.ImageAttribute
 import org.bouncycastle.openpgp.PGPUserAttributeSubpacketVectorGenerator
 import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.assertThrows
 import org.pgpainless.PGPainless
 import org.pgpainless.algorithm.KeyFlag
+import org.pgpainless.algorithm.PublicKeyAlgorithm
 import org.pgpainless.key.generation.type.KeyType
 import org.pgpainless.key.generation.type.eddsa.EdDSACurve
+import org.pgpainless.key.generation.type.rsa.RsaLength
 import org.pgpainless.key.generation.type.xdh.XDHSpec
 import org.pgpainless.key.protection.SecretKeyRingProtector
 import org.pgpainless.policy.Policy
@@ -49,4 +52,23 @@ class OpenPgpKeyBuilderTest {
                 .build()
         println(PGPainless.asciiArmor(key))
     }
+
+    @Test
+    fun testKeyGenerationWithUnacceptablePKAlgorithmFails() {
+        // Policy only allows RSA 4096 algorithms
+        val policy =
+            Policy(
+                publicKeyAlgorithmPolicy =
+                    Policy.PublicKeyAlgorithmPolicy(mapOf(PublicKeyAlgorithm.RSA_GENERAL to 4096)))
+        val builder = OpenPgpKeyBuilder(policy)
+
+        assertThrows<IllegalArgumentException> {
+            builder.buildV4Key(KeyType.RSA(RsaLength._3072)) // too weak
+        }
+
+        val v4Builder = builder.buildV4Key(KeyType.RSA(RsaLength._4096)) // ok
+        assertThrows<IllegalArgumentException> {
+            v4Builder.addSigningSubkey(KeyType.RSA(RsaLength._2048)) // too weak
+        }
+    }
 }