Add support for endpoint checking prekey consistency.

libsignal-service/src/main/java/org/whispersystems/signalservice/api/SignalServiceAccountManager.java

@@ -30,6 +30,7 @@ import org.whispersystems.signalservice.api.groupsv2.ClientZkOperations;
 import org.whispersystems.signalservice.api.groupsv2.GroupsV2Api;
 import org.whispersystems.signalservice.api.groupsv2.GroupsV2Operations;
 import org.whispersystems.signalservice.api.kbs.MasterKey;
+import org.whispersystems.signalservice.api.keys.KeysApi;
 import org.whispersystems.signalservice.api.messages.calls.TurnServerInfo;
 import org.whispersystems.signalservice.api.messages.multidevice.DeviceInfo;
 import org.whispersystems.signalservice.api.payments.CurrencyConversions;
@@ -864,6 +865,10 @@ public class SignalServiceAccountManager {
     return ArchiveApi.create(pushServiceSocket, configuration.getBackupServerPublicParams(), credentials.getAci());
   }
 
+  public KeysApi getKeysApi() {
+    return KeysApi.create(pushServiceSocket);
+  }
+
   public AuthCredentials getPaymentsAuthorization() throws IOException {
     return pushServiceSocket.getPaymentsAuthorization();
   }

libsignal-service/src/main/java/org/whispersystems/signalservice/api/keys/KeysApi.kt

@@ -0,0 +1,57 @@
+/*
+ * Copyright 2024 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.whispersystems.signalservice.api.keys
+
+import org.signal.core.util.toByteArray
+import org.signal.libsignal.protocol.IdentityKey
+import org.signal.libsignal.protocol.ecc.ECPublicKey
+import org.signal.libsignal.protocol.kem.KEMPublicKey
+import org.whispersystems.signalservice.api.NetworkResult
+import org.whispersystems.signalservice.api.push.ServiceIdType
+import org.whispersystems.signalservice.internal.push.PushServiceSocket
+import java.security.MessageDigest
+
+/**
+ * Contains APIs for interacting with /keys endpoints on the service.
+ */
+class KeysApi(private val pushServiceSocket: PushServiceSocket) {
+
+  companion object {
+    @JvmStatic
+    fun create(pushServiceSocket: PushServiceSocket): KeysApi {
+      return KeysApi(pushServiceSocket)
+    }
+  }
+
+  /**
+   * Checks to see if our local view of our repeated-use prekeys matches the server's view. It's an all-or-nothing match, and no details can be given beyond
+   * whether or not everything perfectly matches or not.
+   *
+   * Status codes:
+   * - 200: Everything matches
+   * - 409: Something doesn't match
+   */
+  fun checkRepeatedUseKeys(
+    serviceIdType: ServiceIdType,
+    identityKey: IdentityKey,
+    signedPreKeyId: Int,
+    signedPreKey: ECPublicKey,
+    lastResortKyberKeyId: Int,
+    lastResortKyberKey: KEMPublicKey
+  ): NetworkResult<Unit> {
+    val digest: MessageDigest = MessageDigest.getInstance("SHA-256").apply {
+      update(identityKey.serialize())
+      update(signedPreKeyId.toLong().toByteArray())
+      update(signedPreKey.serialize())
+      update(lastResortKyberKeyId.toLong().toByteArray())
+      update(lastResortKyberKey.serialize())
+    }
+
+    return NetworkResult.fromFetch {
+      pushServiceSocket.checkRepeatedUsePreKeys(serviceIdType, digest.digest())
+    }
+  }
+}

libsignal-service/src/main/java/org/whispersystems/signalservice/internal/push/ByteArrayDeserializerBase64.kt

@@ -0,0 +1,20 @@
+/*
+ * Copyright 2024 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.whispersystems.signalservice.internal.push
+
+import com.fasterxml.jackson.core.JsonParser
+import com.fasterxml.jackson.databind.DeserializationContext
+import com.fasterxml.jackson.databind.JsonDeserializer
+import org.signal.core.util.Base64
+
+/**
+ * Deserializes any valid base64 (regardless of padding or url-safety) into a ByteArray.
+ */
+class ByteArrayDeserializerBase64 : JsonDeserializer<ByteArray>() {
+  override fun deserialize(p: JsonParser, ctxt: DeserializationContext): ByteArray {
+    return Base64.decode(p.valueAsString)
+  }
+}

libsignal-service/src/main/java/org/whispersystems/signalservice/internal/push/ByteArraySerializerBase64NoPadding.kt

@@ -0,0 +1,20 @@
+/*
+ * Copyright 2024 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.whispersystems.signalservice.internal.push
+
+import com.fasterxml.jackson.core.JsonGenerator
+import com.fasterxml.jackson.databind.JsonSerializer
+import com.fasterxml.jackson.databind.SerializerProvider
+import org.signal.core.util.Base64
+
+/**
+ * JSON serializer to encode a ByteArray as a base64 string without padding.
+ */
+class ByteArraySerializerBase64NoPadding : JsonSerializer<ByteArray>() {
+  override fun serialize(value: ByteArray, gen: JsonGenerator, serializers: SerializerProvider) {
+    gen.writeString(Base64.encodeWithoutPadding(value))
+  }
+}

libsignal-service/src/main/java/org/whispersystems/signalservice/internal/push/CheckRepeatedUsedPreKeysRequest.kt

@@ -0,0 +1,21 @@
+/*
+ * Copyright 2024 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.whispersystems.signalservice.internal.push
+
+import com.fasterxml.jackson.annotation.JsonProperty
+import com.fasterxml.jackson.databind.annotation.JsonSerialize
+
+/**
+ * Request body to check if our prekeys match what's on the service.
+ */
+class CheckRepeatedUsedPreKeysRequest(
+  @JsonProperty
+  val identityType: String,
+
+  @JsonProperty
+  @JsonSerialize(using = ByteArraySerializerBase64NoPadding::class)
+  val digest: ByteArray
+)

libsignal-service/src/main/java/org/whispersystems/signalservice/internal/push/PushServiceSocket.java

@@ -231,6 +231,8 @@ public class PushServiceSocket {
   private static final String PREKEY_METADATA_PATH      = "/v2/keys?identity=%s";
   private static final String PREKEY_PATH               = "/v2/keys?identity=%s";
   private static final String PREKEY_DEVICE_PATH        = "/v2/keys/%s/%s?pq=true";
+  private static final String PREKEY_CHECK_PATH        = "/v2/keys/check";
+
 
   private static final String PROVISIONING_CODE_PATH    = "/v1/devices/provisioning/code";
   private static final String PROVISIONING_MESSAGE_PATH = "/v1/provisioning/%s";
@@ -874,6 +876,17 @@ public class PushServiceSocket {
     }
   }
 
+  public void checkRepeatedUsePreKeys(ServiceIdType serviceIdType, byte[] digest) throws IOException {
+    String body = JsonUtil.toJson(new CheckRepeatedUsedPreKeysRequest(serviceIdType.toString(), digest));
+
+    makeServiceRequest(PREKEY_CHECK_PATH, "POST", body, NO_HEADERS, (responseCode, body1) -> {
+      // Must override this handling because otherwise code assumes a device mismatch error
+      if  (responseCode == 409) {
+        throw new NonSuccessfulResponseCodeException(409);
+      }
+    }, Optional.empty());
+  }
+
   public void retrieveAttachment(int cdnNumber, SignalServiceAttachmentRemoteId cdnPath, File destination, long maxSizeBytes, ProgressListener listener)
       throws IOException, MissingConfigurationException
   {