diff --git a/services/identity/Cargo.lock b/services/identity/Cargo.lock
--- a/services/identity/Cargo.lock
+++ b/services/identity/Cargo.lock
@@ -4,9 +4,9 @@
 
 [[package]]
 name = "aho-corasick"
-version = "0.7.20"
+version = "1.0.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "cc936419f96fa211c1b9166887b38e5e40b19958e5b895be7c1f93adec7071ac"
+checksum = "67fc08ce920c31afb70f013dcce1bfc3a3195de6a228474e45e1f145b36f8d04"
 dependencies = [
  "memchr",
 ]
@@ -680,7 +680,7 @@
  "argon2",
  "log",
  "opaque-ke 2.0.0",
- "rand",
+ "rand 0.8.5",
  "tonic",
  "wasm-bindgen",
 ]
@@ -971,6 +971,29 @@
  "signature",
 ]
 
+[[package]]
+name = "ed25519"
+version = "1.5.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "91cff35c70bba8a626e3185d8cd48cc11b5437e1a5bcd15b9b5fa3c64b6dfee7"
+dependencies = [
+ "signature",
+]
+
+[[package]]
+name = "ed25519-dalek"
+version = "1.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c762bae6dcaf24c4c84667b8579785430908723d5c889f469d76a41d59cc7a9d"
+dependencies = [
+ "curve25519-dalek 3.2.0",
+ "ed25519",
+ "rand 0.7.3",
+ "serde",
+ "sha2 0.9.9",
+ "zeroize",
+]
+
 [[package]]
 name = "either"
 version = "1.8.1"
@@ -1461,13 +1484,15 @@
  "constant_time_eq 0.2.5",
  "curve25519-dalek 3.2.0",
  "derive_more",
+ "ed25519-dalek",
  "futures-core",
  "hex",
  "moka",
  "once_cell",
  "opaque-ke 1.2.0",
  "prost",
- "rand",
+ "rand 0.8.5",
+ "regex",
  "serde",
  "serde_json",
  "siwe",
@@ -1772,7 +1797,7 @@
  "getrandom 0.2.9",
  "hkdf 0.11.0",
  "hmac 0.11.0",
- "rand",
+ "rand 0.8.5",
  "subtle",
  "zeroize",
 ]
@@ -1792,7 +1817,7 @@
  "generic-array",
  "hkdf 0.12.3",
  "hmac 0.12.1",
- "rand",
+ "rand 0.8.5",
  "serde",
  "subtle",
  "voprf",
@@ -2066,6 +2091,19 @@
  "proc-macro2",
 ]
 
+[[package]]
+name = "rand"
+version = "0.7.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6a6b1679d49b24bbfe0c803429aa1874472f50d9b363131f0e89fc356b544d03"
+dependencies = [
+ "getrandom 0.1.16",
+ "libc",
+ "rand_chacha 0.2.2",
+ "rand_core 0.5.1",
+ "rand_hc",
+]
+
 [[package]]
 name = "rand"
 version = "0.8.5"
@@ -2073,10 +2111,20 @@
 checksum = "34af8d1a0e25924bc5b7c43c079c942339d8f0a8b57c39049bef581b46327404"
 dependencies = [
  "libc",
- "rand_chacha",
+ "rand_chacha 0.3.1",
  "rand_core 0.6.4",
 ]
 
+[[package]]
+name = "rand_chacha"
+version = "0.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f4c8ed856279c9737206bf725bf36935d8666ead7aa69b52be55af369d193402"
+dependencies = [
+ "ppv-lite86",
+ "rand_core 0.5.1",
+]
+
 [[package]]
 name = "rand_chacha"
 version = "0.3.1"
@@ -2105,6 +2153,15 @@
  "getrandom 0.2.9",
 ]
 
+[[package]]
+name = "rand_hc"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ca3129af7b92a17112d59ad498c6f81eaf463253766b90396d39ea7a39d6613c"
+dependencies = [
+ "rand_core 0.5.1",
+]
+
 [[package]]
 name = "raw-cpuid"
 version = "10.7.0"
@@ -2134,9 +2191,9 @@
 
 [[package]]
 name = "regex"
-version = "1.7.3"
+version = "1.8.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8b1f693b24f6ac912f4893ef08244d70b6067480d2f1a46e950c9691e6749d1d"
+checksum = "81ca098a9821bd52d6b24fd8b10bd081f47d39c22778cafaa75a2857a62c6390"
 dependencies = [
  "aho-corasick",
  "memchr",
@@ -2145,9 +2202,9 @@
 
 [[package]]
 name = "regex-syntax"
-version = "0.6.29"
+version = "0.7.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f162c6dd7b008981e4d40210aca20b4bd0f9b60ca9271061b07f78537722f2e1"
+checksum = "436b050e76ed2903236f032a59761c1eb99e1b0aead2c257922771dab1fc8c78"
 
 [[package]]
 name = "ring"
@@ -2423,7 +2480,7 @@
  "http",
  "iri-string",
  "k256",
- "rand",
+ "rand 0.8.5",
  "sha3",
  "thiserror",
 ]
@@ -2761,7 +2818,7 @@
  "indexmap",
  "pin-project",
  "pin-project-lite",
- "rand",
+ "rand 0.8.5",
  "slab",
  "tokio",
  "tokio-util",
diff --git a/services/identity/Cargo.toml b/services/identity/Cargo.toml
--- a/services/identity/Cargo.toml
+++ b/services/identity/Cargo.toml
@@ -12,6 +12,7 @@
 tokio-stream = "0.1.9"
 opaque-ke = { version = "1.2.0", features = ["std"] }
 curve25519-dalek = "3"
+ed25519-dalek = "1"
 clap = { version = "3.1.12", features = ["derive"] }
 derive_more = "0.99"
 aws-config = "0.54.0"
@@ -32,6 +33,7 @@
 serde_json = "1.0.95"
 moka = { version = "0.10", features = ["future"] }
 uuid = { version = "1.3", features = [ "v4" ] }
+regex = "1.8.3"
 
 [build-dependencies]
 tonic-build = "0.9.1"
diff --git a/services/identity/src/main.rs b/services/identity/src/main.rs
--- a/services/identity/src/main.rs
+++ b/services/identity/src/main.rs
@@ -14,6 +14,7 @@
 mod interceptor;
 mod keygen;
 mod nonce;
+mod reserved_users;
 mod siwe;
 mod token;
 
diff --git a/services/identity/src/reserved_users.rs b/services/identity/src/reserved_users.rs
new file mode 100644
--- /dev/null
+++ b/services/identity/src/reserved_users.rs
@@ -0,0 +1,47 @@
+use std::str::FromStr;
+
+use chrono::{DateTime, Utc};
+use ed25519_dalek::Signature;
+use regex::Regex;
+use tonic::Status;
+use tracing::error;
+
+pub fn validate_signed_keyserver_message(
+  username: &str,
+  keyserver_message: &str,
+  keyserver_signature: &str,
+) -> Result<(), Status> {
+  // Prepare regex to match the keyserver_message string
+  let re = Regex::new(
+    r"^This user is the owner of the following username:\n(.+)\n\nIssued At: ([^Z]+Z)$",
+  ).map_err(|_|{
+    error!("Invalid regex expression");
+    Status::internal("internal error")})?;
+  let caps = match re.captures(keyserver_message) {
+    Some(caps) => caps,
+    None => return Err(Status::invalid_argument("message format invalid")),
+  };
+
+  let message_username = &caps[1];
+  let issued_at: DateTime<Utc> = caps[2]
+    .parse()
+    .map_err(|_| Status::invalid_argument("message format invalid"))?;
+
+  // Check that the username in the gRPC message matches the username in the keyserver_message string
+  if message_username != username {
+    return Err(Status::invalid_argument("message invalid"));
+  }
+
+  // Check that no more than 5 seconds have passed since the timestamp in the keyserver_message string
+  let now = Utc::now();
+  if (now - issued_at).num_seconds() > 5 {
+    return Err(Status::invalid_argument("message invalid"));
+  }
+
+  let _signature = Signature::from_str(keyserver_signature)
+    .map_err(|_| Status::invalid_argument("message invalid"))?;
+
+  // TODO: verify the signature once ashoat's keyserver is registered
+
+  Ok(())
+}