Add an endpoint for checking that clients and the server have a common view of the client's repeated-use keys

service/src/main/java/org/whispersystems/textsecuregcm/entities/CheckKeysRequest.java

@@ -0,0 +1,34 @@
+package org.whispersystems.textsecuregcm.entities;
+
+import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
+import io.swagger.v3.oas.annotations.media.Schema;
+import org.whispersystems.textsecuregcm.identity.IdentityType;
+import org.whispersystems.textsecuregcm.util.ByteArrayAdapter;
+import org.whispersystems.textsecuregcm.util.ExactlySize;
+
+public record CheckKeysRequest(
+    @Schema(requiredMode = Schema.RequiredMode.REQUIRED, description = """
+        The identity type for which to check for a shared view of repeated-use keys
+        """)
+    IdentityType identityType,
+
+    @JsonDeserialize(using = ByteArrayAdapter.Deserializing.class)
+    @ExactlySize(32)
+    @Schema(requiredMode = Schema.RequiredMode.REQUIRED, description = """
+        A 32-byte digest of the client's repeated-use keys for the given identity type. The digest is calculated as:
+              
+        SHA256(identityKeyBytes || signedEcPreKeyId || signedEcPreKeyIdBytes || lastResortKeyId || lastResortKeyBytes)
+              
+        …where the elements of the hash are:
+              
+        - identityKeyBytes: the serialized form of the client's public identity key as produced by libsignal (i.e. one
+          version byte followed by 32 bytes of key material for a total of 33 bytes)
+        - signedEcPreKeyId: an 8-byte, big-endian representation of the ID of the client's signed EC pre-key
+        - signedEcPreKeyBytes: the serialized form of the client's signed EC pre-key as produced by libsignal (i.e. one
+          version byte followed by 32 bytes of key material for a total of 33 bytes)
+        - lastResortKeyId: an 8-byte, big-endian representation of the ID of the client's last-resort Kyber key
+        - lastResortKeyBytes: the serialized form of the client's last-resort Kyber key as produced by libsignal (i.e.
+          one version byte followed by 1568 bytes of key material for a total of 1569 bytes)
+          """)
+    byte[] digest) {
+}