diff --git a/pgpainless-core/src/main/kotlin/org/pgpainless/PGPainless.kt b/pgpainless-core/src/main/kotlin/org/pgpainless/PGPainless.kt
index 896692c2..863a10da 100644
--- a/pgpainless-core/src/main/kotlin/org/pgpainless/PGPainless.kt
+++ b/pgpainless-core/src/main/kotlin/org/pgpainless/PGPainless.kt
@@ -10,7 +10,9 @@ import org.bouncycastle.openpgp.PGPKeyRing
 import org.bouncycastle.openpgp.PGPPublicKeyRing
 import org.bouncycastle.openpgp.PGPSecretKeyRing
 import org.bouncycastle.openpgp.PGPSignature
+import org.bouncycastle.openpgp.api.OpenPGPImplementation
 import org.pgpainless.algorithm.OpenPGPKeyVersion
+import org.pgpainless.bouncycastle.PolicyAdapter
 import org.pgpainless.decryption_verification.DecryptionBuilder
 import org.pgpainless.encryption_signing.EncryptionBuilder
 import org.pgpainless.key.certification.CertifyCertificate
@@ -23,10 +25,24 @@ import org.pgpainless.key.util.KeyRingUtils
 import org.pgpainless.policy.Policy
 import org.pgpainless.util.ArmorUtils
 
-class PGPainless private constructor() {
+class PGPainless(
+    val implementation: OpenPGPImplementation = OpenPGPImplementation.getInstance(),
+    val algorithmPolicy: Policy = Policy.getInstance()
+) {
+
+    init {
+        implementation.setPolicy(
+            PolicyAdapter(algorithmPolicy)) // adapt PGPainless' Policy to BCs OpenPGPPolicy
+    }
 
     companion object {
 
+        @Volatile private var instance: PGPainless? = null
+
+        @JvmStatic
+        fun getInstance() =
+            instance ?: synchronized(this) { instance ?: PGPainless().also { instance = it } }
+
         /**
          * Generate a fresh OpenPGP key ring from predefined templates.
          *
@@ -166,7 +182,7 @@ class PGPainless private constructor() {
          *
          * @return policy
          */
-        @JvmStatic fun getPolicy() = Policy.getInstance()
+        @JvmStatic fun getPolicy() = getInstance().algorithmPolicy
 
         /**
          * Create different kinds of signatures on other keys.
diff --git a/pgpainless-core/src/main/kotlin/org/pgpainless/bouncycastle/PolicyAdapter.kt b/pgpainless-core/src/main/kotlin/org/pgpainless/bouncycastle/PolicyAdapter.kt
new file mode 100644
index 00000000..eed5e24c
--- /dev/null
+++ b/pgpainless-core/src/main/kotlin/org/pgpainless/bouncycastle/PolicyAdapter.kt
@@ -0,0 +1,77 @@
+// SPDX-FileCopyrightText: 2025 Paul Schaub <vanitasvitae@fsfe.org>
+//
+// SPDX-License-Identifier: Apache-2.0
+
+package org.pgpainless.bouncycastle
+
+import java.util.Date
+import org.bouncycastle.openpgp.api.OpenPGPPolicy
+import org.bouncycastle.openpgp.api.OpenPGPPolicy.OpenPGPNotationRegistry
+import org.pgpainless.policy.Policy
+
+class PolicyAdapter(val policy: Policy = Policy.getInstance()) : OpenPGPPolicy {
+
+    override fun isAcceptableDocumentSignatureHashAlgorithm(
+        algorithmId: Int,
+        signatureCreationTime: Date?
+    ): Boolean {
+        return if (signatureCreationTime == null)
+            policy.dataSignatureHashAlgorithmPolicy.isAcceptable(algorithmId)
+        else
+            policy.dataSignatureHashAlgorithmPolicy.isAcceptable(algorithmId, signatureCreationTime)
+    }
+
+    override fun isAcceptableRevocationSignatureHashAlgorithm(
+        algorithmId: Int,
+        revocationCreationTime: Date?
+    ): Boolean {
+        return if (revocationCreationTime == null)
+            policy.revocationSignatureHashAlgorithmPolicy.isAcceptable(algorithmId)
+        else
+            policy.revocationSignatureHashAlgorithmPolicy.isAcceptable(
+                algorithmId, revocationCreationTime)
+    }
+
+    override fun isAcceptableCertificationSignatureHashAlgorithm(
+        algorithmId: Int,
+        certificationCreationTime: Date?
+    ): Boolean {
+        return if (certificationCreationTime == null)
+            policy.certificationSignatureHashAlgorithmPolicy.isAcceptable(algorithmId)
+        else
+            policy.certificationSignatureHashAlgorithmPolicy.isAcceptable(
+                algorithmId, certificationCreationTime)
+    }
+
+    override fun getDefaultCertificationSignatureHashAlgorithm(): Int {
+        return policy.certificationSignatureHashAlgorithmPolicy.defaultHashAlgorithm.algorithmId
+    }
+
+    override fun getDefaultDocumentSignatureHashAlgorithm(): Int {
+        return policy.dataSignatureHashAlgorithmPolicy.defaultHashAlgorithm.algorithmId
+    }
+
+    override fun isAcceptableSymmetricKeyAlgorithm(p0: Int): Boolean {
+        return policy.symmetricKeyEncryptionAlgorithmPolicy.isAcceptable(p0)
+    }
+
+    override fun getDefaultSymmetricKeyAlgorithm(): Int {
+        return policy.symmetricKeyEncryptionAlgorithmPolicy.defaultSymmetricKeyAlgorithm.algorithmId
+    }
+
+    override fun isAcceptablePublicKeyStrength(algorithmId: Int, bitStrength: Int): Boolean {
+        return policy.publicKeyAlgorithmPolicy.isAcceptable(algorithmId, bitStrength)
+    }
+
+    override fun getNotationRegistry(): OpenPGPPolicy.OpenPGPNotationRegistry {
+        return object : OpenPGPNotationRegistry() {
+            override fun isNotationKnown(notationName: String?): Boolean {
+                return notationName?.let { policy.notationRegistry.isKnownNotation(it) } ?: false
+            }
+
+            override fun addKnownNotation(notationName: String?) {
+                notationName?.let { policy.notationRegistry.addKnownNotation(it) }
+            }
+        }
+    }
+}