diff --git a/pgpainless-wot/src/main/kotlin/org/pgpainless/wot/KeyRingCertificateStore.kt b/pgpainless-wot/src/main/kotlin/org/pgpainless/wot/KeyRingCertificateStore.kt
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+// SPDX-FileCopyrightText: 2023 Paul Schaub <vanitasvitae@fsfe.org>
+//
+// SPDX-License-Identifier: Apache-2.0
+
+package org.pgpainless.wot
+
+import org.bouncycastle.openpgp.PGPPublicKeyRingCollection
+import org.pgpainless.PGPainless
+import org.pgpainless.certificate_store.CertificateFactory
+import org.pgpainless.key.OpenPgpFingerprint
+import pgp.certificate_store.PGPCertificateStore
+import pgp.certificate_store.certificate.Certificate
+import pgp.certificate_store.certificate.KeyMaterialMerger
+import pgp.certificate_store.exception.BadNameException
+import java.io.InputStream
+
+/**
+ * Implementation of [PGPCertificateStore] which is based on a [PGPPublicKeyRingCollection].
+ * During initialization, all items in the [PGPPublicKeyRingCollection] are converted into [Certificates][Certificate]
+ * and stored in a map keyed by their fingerprints.
+ * [Certificates][Certificate] being inserted using [insertCertificate] or [insertCertificateBySpecialName] are also
+ * stored in that map, but are not being written into the [PGPPublicKeyRingCollection].
+ */
+class KeyRingCertificateStore(baseKeyRing: PGPPublicKeyRingCollection) : PGPCertificateStore {
+
+    // Keep certificates inserted only in memory
+    private val certificates = mutableMapOf<String, Certificate>()
+
+    init {
+        for (publicKeyRing in baseKeyRing) {
+            val fingerprint = OpenPgpFingerprint.of(publicKeyRing).toString()
+            val certificate = CertificateFactory.certificateFromPublicKeyRing(publicKeyRing, null)
+            certificates[fingerprint] = certificate
+        }
+    }
+
+    override fun getCertificate(identifier: String?): Certificate {
+        if (identifier == null) {
+            throw BadNameException("Identifier MUST NOT be null.")
+        }
+
+        return certificates.getOrElse(identifier) {
+            throw NoSuchElementException("No certificate for identifier $identifier found.")
+        }
+    }
+
+    override fun getCertificateIfChanged(identifier: String?, tag: Long?): Certificate {
+        return getCertificate(identifier) // TODO: Implement properly
+    }
+
+    override fun getCertificatesBySubkeyId(subkeyId: Long): MutableIterator<Certificate> {
+        return certificates.values.filter {
+            it.subkeyIds.contains(subkeyId)
+        }.toMutableList().listIterator()
+    }
+
+    override fun insertCertificate(data: InputStream?, merge: KeyMaterialMerger?): Certificate {
+        val publicKeys = PGPainless.readKeyRing().publicKeyRing(data!!)
+        val certificate = CertificateFactory.certificateFromPublicKeyRing(publicKeys!!, null)
+        var insert: Certificate? = if (merge != null) {
+            val existing = try {
+                getCertificate(certificate.fingerprint)
+            } catch (e: NoSuchElementException) {
+                null
+            }
+            merge.merge(certificate, existing).asCertificate()
+        } else {
+            certificate
+        }
+
+        if (insert == null) {
+            return certificate
+        }
+
+        certificates[insert.fingerprint] = insert
+        return insert
+    }
+
+    override fun insertCertificateBySpecialName(specialName: String?, data: InputStream?, merge: KeyMaterialMerger?): Certificate {
+        val publicKeys = PGPainless.readKeyRing().publicKeyRing(data!!)
+        val certificate = CertificateFactory.certificateFromPublicKeyRing(publicKeys!!, null)
+
+        var insert: Certificate? = if (merge != null) {
+            val existing = try {
+                getCertificate(specialName!!)
+            } catch (e: NoSuchElementException) {
+                null
+            }
+            merge.merge(certificate, existing).asCertificate()
+        } else {
+            certificate
+        }
+
+        if (insert == null) {
+            return certificate
+        }
+
+        certificates[specialName!!] = insert
+        return insert
+    }
+
+    override fun getCertificates(): MutableIterator<Certificate> {
+        return certificates.values.iterator()
+    }
+
+    override fun getFingerprints(): MutableIterator<String> {
+        return certificates.values.map { it.fingerprint }.toMutableList().listIterator()
+    }
+
+}
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