diff --git a/services/identity/src/constants.rs b/services/identity/src/constants.rs
index 3b61f725b..e3b5a7980 100644
--- a/services/identity/src/constants.rs
+++ b/services/identity/src/constants.rs
@@ -1,105 +1,109 @@
 // Secrets
 
 pub const SECRETS_DIRECTORY: &str = "secrets";
 pub const SECRETS_FILE_NAME: &str = "secret_key";
 pub const SECRETS_FILE_EXTENSION: &str = "txt";
 pub const SECRETS_SETUP_FILE: &str = "server_setup.txt";
 
 // DynamoDB
 
 // User table information, supporting opaque_ke 2.0 and X3DH information
 
 // Users can sign in either through username+password or Eth wallet.
 //
 // This structure should be aligned with the messages defined in
 // shared/protos/identity_client.proto
 //
 // Structure for a user should be:
 // {
 //   userID: String,
 //   opaqueRegistrationData: Option<String>,
 //   username: Option<String>,
 //   walletAddress: Option<String>,
 //   devices: HashMap<String, Device>
 // }
 //
 // A device is defined as:
 // {
 //     deviceType: String, # client or keyserver
 //     keyPayload: String,
 //     keyPayloadSignature: String,
 //     identityPreKey: String,
 //     identityPreKeySignature: String,
 //     identityOneTimeKeys: Vec<String>,
 //     notifPreKey: String,
 //     notifPreKeySignature: String,
 //     notifOneTimeKeys: Vec<String>,
 //     socialProof: Option<String>
 //   }
 // }
 //
 // Additional context:
 // "devices" uses the signing public identity key of the device as a key for the devices map
 // "keyPayload" is a JSON encoded string containing identity and notif keys (both signature and verification)
 // if "deviceType" == "keyserver", then the device will not have any notif key information
 
 pub const USERS_TABLE: &str = "identity-users";
 pub const USERS_TABLE_PARTITION_KEY: &str = "userID";
 pub const USERS_TABLE_REGISTRATION_ATTRIBUTE: &str = "opaqueRegistrationData";
 pub const USERS_TABLE_USERNAME_ATTRIBUTE: &str = "username";
 pub const USERS_TABLE_DEVICES_ATTRIBUTE: &str = "devices";
 pub const USERS_TABLE_DEVICES_MAP_DEVICE_TYPE_ATTRIBUTE_NAME: &str =
   "deviceType";
 pub const USERS_TABLE_DEVICES_MAP_KEY_PAYLOAD_ATTRIBUTE_NAME: &str =
   "keyPayload";
 pub const USERS_TABLE_DEVICES_MAP_KEY_PAYLOAD_SIGNATURE_ATTRIBUTE_NAME: &str =
   "keyPayloadSignature";
 pub const USERS_TABLE_DEVICES_MAP_CONTENT_PREKEY_ATTRIBUTE_NAME: &str =
   "identityPreKey";
 pub const USERS_TABLE_DEVICES_MAP_CONTENT_PREKEY_SIGNATURE_ATTRIBUTE_NAME:
   &str = "identityPreKeySignature";
 pub const USERS_TABLE_DEVICES_MAP_CONTENT_ONETIME_KEYS_ATTRIBUTE_NAME: &str =
   "identityOneTimeKeys";
 pub const USERS_TABLE_DEVICES_MAP_NOTIF_PREKEY_ATTRIBUTE_NAME: &str = "preKey";
 pub const USERS_TABLE_DEVICES_MAP_NOTIF_PREKEY_SIGNATURE_ATTRIBUTE_NAME: &str =
   "preKeySignature";
 pub const USERS_TABLE_DEVICES_MAP_NOTIF_ONETIME_KEYS_ATTRIBUTE_NAME: &str =
   "notifOneTimeKeys";
 pub const USERS_TABLE_WALLET_ADDRESS_ATTRIBUTE: &str = "walletAddress";
 pub const USERS_TABLE_DEVICES_MAP_SOCIAL_PROOF_ATTRIBUTE_NAME: &str =
   "socialProof";
 pub const USERS_TABLE_USERNAME_INDEX: &str = "username-index";
 pub const USERS_TABLE_WALLET_ADDRESS_INDEX: &str = "walletAddress-index";
 
 pub const ACCESS_TOKEN_TABLE: &str = "identity-tokens";
 pub const ACCESS_TOKEN_TABLE_PARTITION_KEY: &str = "userID";
 pub const ACCESS_TOKEN_SORT_KEY: &str = "signingPublicKey";
 pub const ACCESS_TOKEN_TABLE_CREATED_ATTRIBUTE: &str = "created";
 pub const ACCESS_TOKEN_TABLE_AUTH_TYPE_ATTRIBUTE: &str = "authType";
 pub const ACCESS_TOKEN_TABLE_VALID_ATTRIBUTE: &str = "valid";
 pub const ACCESS_TOKEN_TABLE_TOKEN_ATTRIBUTE: &str = "token";
 
 pub const NONCE_TABLE: &str = "identity-nonces";
 pub const NONCE_TABLE_PARTITION_KEY: &str = "nonce";
 pub const NONCE_TABLE_CREATED_ATTRIBUTE: &str = "created";
 
+// Usernames reserved because they exist in Ashoat's keyserver already
+pub const RESERVED_USERNAMES_TABLE: &str = "identity-reserved-usernames";
+pub const RESERVED_USERNAMES_TABLE_PARTITION_KEY: &str = "username";
+
 // Tokio
 
 pub const MPSC_CHANNEL_BUFFER_CAPACITY: usize = 1;
 pub const IDENTITY_SERVICE_SOCKET_ADDR: &str = "[::]:50054";
 
 // Token
 
 pub const ACCESS_TOKEN_LENGTH: usize = 512;
 
 // Temporary config
 
 pub const AUTH_TOKEN: &str = "COMM_IDENTITY_SERVICE_AUTH_TOKEN";
 
 // Nonce
 
 pub const NONCE_LENGTH: usize = 17;
 
 // LocalStack
 
 pub const LOCALSTACK_ENDPOINT: &str = "LOCALSTACK_ENDPOINT";
diff --git a/services/identity/src/database.rs b/services/identity/src/database.rs
index 2e8269a3b..d863ad23d 100644
--- a/services/identity/src/database.rs
+++ b/services/identity/src/database.rs
@@ -1,923 +1,998 @@
 use std::collections::HashMap;
 use std::fmt::{Display, Formatter, Result as FmtResult};
 use std::str::FromStr;
 use std::sync::Arc;
 
 use aws_config::SdkConfig;
 use aws_sdk_dynamodb::model::AttributeValue;
 use aws_sdk_dynamodb::output::{
   DeleteItemOutput, GetItemOutput, PutItemOutput, QueryOutput,
 };
 use aws_sdk_dynamodb::types::Blob;
 use aws_sdk_dynamodb::{Client, Error as DynamoDBError};
 use chrono::{DateTime, Utc};
 use opaque_ke::errors::ProtocolError;
 use serde::{Deserialize, Serialize};
 use tracing::{debug, error, info, warn};
 
 use crate::client_service::{FlattenedDeviceKeyUpload, UserRegistrationInfo};
 use crate::config::CONFIG;
 use crate::constants::{
   ACCESS_TOKEN_SORT_KEY, ACCESS_TOKEN_TABLE,
   ACCESS_TOKEN_TABLE_AUTH_TYPE_ATTRIBUTE, ACCESS_TOKEN_TABLE_CREATED_ATTRIBUTE,
   ACCESS_TOKEN_TABLE_PARTITION_KEY, ACCESS_TOKEN_TABLE_TOKEN_ATTRIBUTE,
   ACCESS_TOKEN_TABLE_VALID_ATTRIBUTE, NONCE_TABLE,
-  NONCE_TABLE_CREATED_ATTRIBUTE, NONCE_TABLE_PARTITION_KEY, USERS_TABLE,
-  USERS_TABLE_DEVICES_ATTRIBUTE,
+  NONCE_TABLE_CREATED_ATTRIBUTE, NONCE_TABLE_PARTITION_KEY,
+  RESERVED_USERNAMES_TABLE, RESERVED_USERNAMES_TABLE_PARTITION_KEY,
+  USERS_TABLE, USERS_TABLE_DEVICES_ATTRIBUTE,
   USERS_TABLE_DEVICES_MAP_CONTENT_ONETIME_KEYS_ATTRIBUTE_NAME,
   USERS_TABLE_DEVICES_MAP_CONTENT_PREKEY_ATTRIBUTE_NAME,
   USERS_TABLE_DEVICES_MAP_CONTENT_PREKEY_SIGNATURE_ATTRIBUTE_NAME,
   USERS_TABLE_DEVICES_MAP_DEVICE_TYPE_ATTRIBUTE_NAME,
   USERS_TABLE_DEVICES_MAP_KEY_PAYLOAD_ATTRIBUTE_NAME,
   USERS_TABLE_DEVICES_MAP_KEY_PAYLOAD_SIGNATURE_ATTRIBUTE_NAME,
   USERS_TABLE_DEVICES_MAP_NOTIF_ONETIME_KEYS_ATTRIBUTE_NAME,
   USERS_TABLE_DEVICES_MAP_NOTIF_PREKEY_ATTRIBUTE_NAME,
   USERS_TABLE_DEVICES_MAP_NOTIF_PREKEY_SIGNATURE_ATTRIBUTE_NAME,
   USERS_TABLE_DEVICES_MAP_SOCIAL_PROOF_ATTRIBUTE_NAME,
   USERS_TABLE_PARTITION_KEY, USERS_TABLE_REGISTRATION_ATTRIBUTE,
   USERS_TABLE_USERNAME_ATTRIBUTE, USERS_TABLE_USERNAME_INDEX,
   USERS_TABLE_WALLET_ADDRESS_ATTRIBUTE, USERS_TABLE_WALLET_ADDRESS_INDEX,
 };
 use crate::id::generate_uuid;
 use crate::nonce::NonceData;
 use crate::token::{AccessTokenData, AuthType};
 
 #[derive(Serialize, Deserialize)]
 pub struct OlmKeys {
   pub curve25519: String,
   pub ed25519: String,
 }
 
 #[derive(Serialize, Deserialize)]
 #[serde(rename_all = "camelCase")]
 pub struct KeyPayload {
   pub notification_identity_public_keys: OlmKeys,
   pub primary_identity_public_keys: OlmKeys,
 }
 
 impl FromStr for KeyPayload {
   type Err = serde_json::Error;
 
   // The payload is held in the database as an escaped JSON payload.
   // Escaped double quotes need to be trimmed before attempting to serialize
   fn from_str(payload: &str) -> Result<KeyPayload, Self::Err> {
     serde_json::from_str(&payload.replace(r#"\""#, r#"""#))
   }
 }
 
 pub enum Device {
   Client,
   Keyserver,
 }
 
 impl Display for Device {
   fn fmt(&self, f: &mut Formatter) -> FmtResult {
     match self {
       Device::Client => write!(f, "client"),
       Device::Keyserver => write!(f, "keyserver"),
     }
   }
 }
 
 #[derive(Clone)]
 pub struct DatabaseClient {
   client: Arc<Client>,
 }
 
 impl DatabaseClient {
   pub fn new(aws_config: &SdkConfig) -> Self {
     let client = match &CONFIG.localstack_endpoint {
       Some(endpoint) => {
         info!(
           "Configuring DynamoDB client to use LocalStack endpoint: {}",
           endpoint
         );
         let ddb_config_builder =
           aws_sdk_dynamodb::config::Builder::from(aws_config)
             .endpoint_url(endpoint);
         Client::from_conf(ddb_config_builder.build())
       }
       None => Client::new(aws_config),
     };
 
     DatabaseClient {
       client: Arc::new(client),
     }
   }
 
   pub async fn add_password_user_to_users_table(
     &self,
     registration_state: UserRegistrationInfo,
     password_file: Vec<u8>,
   ) -> Result<String, Error> {
     self
       .add_user_to_users_table(
         registration_state.flattened_device_key_upload,
         Some((registration_state.username, Blob::new(password_file))),
         None,
         None,
       )
       .await
   }
 
   pub async fn add_wallet_user_to_users_table(
     &self,
     flattened_device_key_upload: FlattenedDeviceKeyUpload,
     wallet_address: String,
     social_proof: String,
   ) -> Result<String, Error> {
     self
       .add_user_to_users_table(
         flattened_device_key_upload,
         None,
         Some(wallet_address),
         Some(social_proof),
       )
       .await
   }
 
   async fn add_user_to_users_table(
     &self,
     flattened_device_key_upload: FlattenedDeviceKeyUpload,
     username_and_password_file: Option<(String, Blob)>,
     wallet_address: Option<String>,
     social_proof: Option<String>,
   ) -> Result<String, Error> {
     let user_id = generate_uuid();
     let device_info =
       create_device_info(flattened_device_key_upload.clone(), social_proof);
     let devices = HashMap::from([(
       flattened_device_key_upload.device_id_key,
       AttributeValue::M(device_info),
     )]);
     let mut user = HashMap::from([
       (
         USERS_TABLE_PARTITION_KEY.to_string(),
         AttributeValue::S(user_id.clone()),
       ),
       (
         USERS_TABLE_DEVICES_ATTRIBUTE.to_string(),
         AttributeValue::M(devices),
       ),
     ]);
 
     if let Some((username, password_file)) = username_and_password_file {
       user.insert(
         USERS_TABLE_USERNAME_ATTRIBUTE.to_string(),
         AttributeValue::S(username),
       );
       user.insert(
         USERS_TABLE_REGISTRATION_ATTRIBUTE.to_string(),
         AttributeValue::B(password_file),
       );
     }
 
     if let Some(address) = wallet_address {
       user.insert(
         USERS_TABLE_WALLET_ADDRESS_ATTRIBUTE.to_string(),
         AttributeValue::S(address),
       );
     }
 
     self
       .client
       .put_item()
       .table_name(USERS_TABLE)
       .set_item(Some(user))
       .send()
       .await
       .map_err(|e| Error::AwsSdk(e.into()))?;
 
     Ok(user_id)
   }
 
   pub async fn add_password_user_device_to_users_table(
     &self,
     user_id: String,
     flattened_device_key_upload: FlattenedDeviceKeyUpload,
   ) -> Result<(), Error> {
     self
       .add_device_to_users_table(user_id, flattened_device_key_upload, None)
       .await
   }
 
   pub async fn add_wallet_user_device_to_users_table(
     &self,
     user_id: String,
     flattened_device_key_upload: FlattenedDeviceKeyUpload,
     social_proof: String,
   ) -> Result<(), Error> {
     self
       .add_device_to_users_table(
         user_id,
         flattened_device_key_upload,
         Some(social_proof),
       )
       .await
   }
 
   async fn add_device_to_users_table(
     &self,
     user_id: String,
     flattened_device_key_upload: FlattenedDeviceKeyUpload,
     social_proof: Option<String>,
   ) -> Result<(), Error> {
     let device_info =
       create_device_info(flattened_device_key_upload.clone(), social_proof);
     let update_expression =
       format!("SET {}.#{} = :v", USERS_TABLE_DEVICES_ATTRIBUTE, "deviceID",);
     let expression_attribute_names = HashMap::from([(
       format!("#{}", "deviceID"),
       flattened_device_key_upload.device_id_key,
     )]);
     let expression_attribute_values =
       HashMap::from([(":v".to_string(), AttributeValue::M(device_info))]);
 
     self
       .client
       .update_item()
       .table_name(USERS_TABLE)
       .key(USERS_TABLE_PARTITION_KEY, AttributeValue::S(user_id))
       .update_expression(update_expression)
       .set_expression_attribute_names(Some(expression_attribute_names))
       .set_expression_attribute_values(Some(expression_attribute_values))
       .send()
       .await
       .map_err(|e| Error::AwsSdk(e.into()))?;
 
     Ok(())
   }
 
   pub async fn update_user_password(
     &self,
     user_id: String,
     password_file: Vec<u8>,
   ) -> Result<(), Error> {
     let update_expression =
       format!("SET {} = :p", USERS_TABLE_REGISTRATION_ATTRIBUTE);
     let expression_attribute_values = HashMap::from([(
       ":p".to_string(),
       AttributeValue::B(Blob::new(password_file)),
     )]);
 
     self
       .client
       .update_item()
       .table_name(USERS_TABLE)
       .key(USERS_TABLE_PARTITION_KEY, AttributeValue::S(user_id))
       .update_expression(update_expression)
       .set_expression_attribute_values(Some(expression_attribute_values))
       .send()
       .await
       .map_err(|e| Error::AwsSdk(e.into()))?;
 
     Ok(())
   }
 
   pub async fn delete_user(
     &self,
     user_id: String,
   ) -> Result<DeleteItemOutput, Error> {
     debug!("Attempting to delete user: {}", user_id);
 
     match self
       .client
       .delete_item()
       .table_name(USERS_TABLE)
       .key(
         USERS_TABLE_PARTITION_KEY,
         AttributeValue::S(user_id.clone()),
       )
       .send()
       .await
     {
       Ok(out) => {
         info!("User has been deleted {}", user_id);
         Ok(out)
       }
       Err(e) => {
         error!("DynamoDB client failed to delete user {}", user_id);
         Err(Error::AwsSdk(e.into()))
       }
     }
   }
 
   pub async fn get_access_token_data(
     &self,
     user_id: String,
     signing_public_key: String,
   ) -> Result<Option<AccessTokenData>, Error> {
     let primary_key = create_composite_primary_key(
       (
         ACCESS_TOKEN_TABLE_PARTITION_KEY.to_string(),
         user_id.clone(),
       ),
       (
         ACCESS_TOKEN_SORT_KEY.to_string(),
         signing_public_key.clone(),
       ),
     );
     let get_item_result = self
       .client
       .get_item()
       .table_name(ACCESS_TOKEN_TABLE)
       .set_key(Some(primary_key))
       .consistent_read(true)
       .send()
       .await;
     match get_item_result {
       Ok(GetItemOutput {
         item: Some(mut item),
         ..
       }) => {
         let created = parse_created_attribute(
           item.remove(ACCESS_TOKEN_TABLE_CREATED_ATTRIBUTE),
         )?;
         let auth_type = parse_auth_type_attribute(
           item.remove(ACCESS_TOKEN_TABLE_AUTH_TYPE_ATTRIBUTE),
         )?;
         let valid = parse_valid_attribute(
           item.remove(ACCESS_TOKEN_TABLE_VALID_ATTRIBUTE),
         )?;
         let access_token = parse_token_attribute(
           item.remove(ACCESS_TOKEN_TABLE_TOKEN_ATTRIBUTE),
         )?;
         Ok(Some(AccessTokenData {
           user_id,
           signing_public_key,
           access_token,
           created,
           auth_type,
           valid,
         }))
       }
       Ok(_) => {
         info!(
           "No item found for user {} and signing public key {} in token table",
           user_id, signing_public_key
         );
         Ok(None)
       }
       Err(e) => {
         error!(
           "DynamoDB client failed to get token for user {} with signing public key {}: {}",
           user_id, signing_public_key, e
         );
         Err(Error::AwsSdk(e.into()))
       }
     }
   }
 
   pub async fn put_access_token_data(
     &self,
     access_token_data: AccessTokenData,
   ) -> Result<PutItemOutput, Error> {
     let item = HashMap::from([
       (
         ACCESS_TOKEN_TABLE_PARTITION_KEY.to_string(),
         AttributeValue::S(access_token_data.user_id),
       ),
       (
         ACCESS_TOKEN_SORT_KEY.to_string(),
         AttributeValue::S(access_token_data.signing_public_key),
       ),
       (
         ACCESS_TOKEN_TABLE_TOKEN_ATTRIBUTE.to_string(),
         AttributeValue::S(access_token_data.access_token),
       ),
       (
         ACCESS_TOKEN_TABLE_CREATED_ATTRIBUTE.to_string(),
         AttributeValue::S(access_token_data.created.to_rfc3339()),
       ),
       (
         ACCESS_TOKEN_TABLE_AUTH_TYPE_ATTRIBUTE.to_string(),
         AttributeValue::S(match access_token_data.auth_type {
           AuthType::Password => "password".to_string(),
           AuthType::Wallet => "wallet".to_string(),
         }),
       ),
       (
         ACCESS_TOKEN_TABLE_VALID_ATTRIBUTE.to_string(),
         AttributeValue::Bool(access_token_data.valid),
       ),
     ]);
     self
       .client
       .put_item()
       .table_name(ACCESS_TOKEN_TABLE)
       .set_item(Some(item))
       .send()
       .await
       .map_err(|e| Error::AwsSdk(e.into()))
   }
 
   pub async fn username_taken(&self, username: String) -> Result<bool, Error> {
     let result = self
       .get_user_id_from_user_info(username, AuthType::Password)
       .await?;
 
     Ok(result.is_some())
   }
 
   async fn get_user_from_user_info(
     &self,
     user_info: String,
     auth_type: AuthType,
   ) -> Result<Option<HashMap<String, AttributeValue>>, Error> {
     let (index, attribute_name) = match auth_type {
       AuthType::Password => {
         (USERS_TABLE_USERNAME_INDEX, USERS_TABLE_USERNAME_ATTRIBUTE)
       }
       AuthType::Wallet => (
         USERS_TABLE_WALLET_ADDRESS_INDEX,
         USERS_TABLE_WALLET_ADDRESS_ATTRIBUTE,
       ),
     };
     match self
       .client
       .query()
       .table_name(USERS_TABLE)
       .index_name(index)
       .key_condition_expression(format!("{} = :u", attribute_name))
       .expression_attribute_values(":u", AttributeValue::S(user_info.clone()))
       .send()
       .await
     {
       Ok(QueryOutput {
         items: Some(items), ..
       }) => {
         let num_items = items.len();
         if num_items == 0 {
           return Ok(None);
         }
         if num_items > 1 {
           warn!(
             "{} user IDs associated with {} {}: {:?}",
             num_items, attribute_name, user_info, items
           );
         }
         let first_item = items[0].clone();
         Ok(Some(first_item))
       }
       Ok(_) => {
         info!(
           "No item found for {} {} in users table",
           attribute_name, user_info
         );
         Ok(None)
       }
       Err(e) => {
         error!(
           "DynamoDB client failed to get user from {} {}: {}",
           attribute_name, user_info, e
         );
         Err(Error::AwsSdk(e.into()))
       }
     }
   }
 
   pub async fn get_user_id_from_user_info(
     &self,
     user_info: String,
     auth_type: AuthType,
   ) -> Result<Option<String>, Error> {
     match self
       .get_user_from_user_info(user_info.clone(), auth_type)
       .await
     {
       Ok(Some(mut user)) => parse_string_attribute(
         USERS_TABLE_PARTITION_KEY,
         user.remove(USERS_TABLE_PARTITION_KEY),
       )
       .map(Some)
       .map_err(Error::Attribute),
       Ok(_) => Ok(None),
       Err(e) => Err(e),
     }
   }
 
   pub async fn get_user_id_and_password_file_from_username(
     &self,
     username: &str,
   ) -> Result<Option<(String, Vec<u8>)>, Error> {
     match self
       .get_user_from_user_info(username.to_string(), AuthType::Password)
       .await
     {
       Ok(Some(mut user)) => {
         let user_id = parse_string_attribute(
           USERS_TABLE_PARTITION_KEY,
           user.remove(USERS_TABLE_PARTITION_KEY),
         )?;
         let password_file = parse_registration_data_attribute(
           user.remove(USERS_TABLE_REGISTRATION_ATTRIBUTE),
         )?;
 
         Ok(Some((user_id, password_file)))
       }
       Ok(_) => {
         info!(
           "No item found for user {} in PAKE registration table",
           username
         );
         Ok(None)
       }
       Err(e) => {
         error!(
           "DynamoDB client failed to get registration data for user {}: {}",
           username, e
         );
         Err(e)
       }
     }
   }
 
   pub async fn get_item_from_users_table(
     &self,
     user_id: &str,
   ) -> Result<GetItemOutput, Error> {
     let primary_key = create_simple_primary_key((
       USERS_TABLE_PARTITION_KEY.to_string(),
       user_id.to_string(),
     ));
     self
       .client
       .get_item()
       .table_name(USERS_TABLE)
       .set_key(Some(primary_key))
       .consistent_read(true)
       .send()
       .await
       .map_err(|e| Error::AwsSdk(e.into()))
   }
 
   pub async fn get_users(&self) -> Result<Vec<String>, Error> {
     let scan_output = self
       .client
       .scan()
       .table_name(USERS_TABLE)
       .projection_expression(USERS_TABLE_PARTITION_KEY)
       .send()
       .await
       .map_err(|e| Error::AwsSdk(e.into()))?;
 
     let mut result = Vec::new();
     if let Some(attributes) = scan_output.items {
       for mut attribute in attributes {
         let id = parse_string_attribute(
           USERS_TABLE_PARTITION_KEY,
           attribute.remove(USERS_TABLE_PARTITION_KEY),
         )
         .map_err(Error::Attribute)?;
         result.push(id);
       }
     }
     Ok(result)
   }
 
   pub async fn add_nonce_to_nonces_table(
     &self,
     nonce_data: NonceData,
   ) -> Result<PutItemOutput, Error> {
     let item = HashMap::from([
       (
         NONCE_TABLE_PARTITION_KEY.to_string(),
         AttributeValue::S(nonce_data.nonce),
       ),
       (
         NONCE_TABLE_CREATED_ATTRIBUTE.to_string(),
         AttributeValue::S(nonce_data.created.to_rfc3339()),
       ),
     ]);
     self
       .client
       .put_item()
       .table_name(NONCE_TABLE)
       .set_item(Some(item))
       .send()
       .await
       .map_err(|e| Error::AwsSdk(e.into()))
   }
+
+  pub async fn add_username_to_reserved_usernames_table(
+    &self,
+    username: String,
+  ) -> Result<PutItemOutput, Error> {
+    let item = HashMap::from([(
+      RESERVED_USERNAMES_TABLE_PARTITION_KEY.to_string(),
+      AttributeValue::S(username),
+    )]);
+    self
+      .client
+      .put_item()
+      .table_name(RESERVED_USERNAMES_TABLE)
+      .set_item(Some(item))
+      .send()
+      .await
+      .map_err(|e| Error::AwsSdk(e.into()))
+  }
+
+  pub async fn delete_username_from_reserved_usernames_table(
+    &self,
+    username: String,
+  ) -> Result<DeleteItemOutput, Error> {
+    debug!(
+      "Attempting to delete username {} from reserved usernames table",
+      username
+    );
+
+    match self
+      .client
+      .delete_item()
+      .table_name(RESERVED_USERNAMES_TABLE)
+      .key(
+        RESERVED_USERNAMES_TABLE_PARTITION_KEY,
+        AttributeValue::S(username.clone()),
+      )
+      .send()
+      .await
+    {
+      Ok(out) => {
+        info!(
+          "Username {} has been deleted from reserved usernames table",
+          username
+        );
+        Ok(out)
+      }
+      Err(e) => {
+        error!("DynamoDB client failed to delete username {} from reserved usernames table", username);
+        Err(Error::AwsSdk(e.into()))
+      }
+    }
+  }
+
+  pub async fn username_in_reserved_usernames_table(
+    &self,
+    username: &str,
+  ) -> Result<bool, Error> {
+    match self
+      .client
+      .get_item()
+      .table_name(RESERVED_USERNAMES_TABLE)
+      .key(
+        RESERVED_USERNAMES_TABLE_PARTITION_KEY.to_string(),
+        AttributeValue::S(username.to_string()),
+      )
+      .consistent_read(true)
+      .send()
+      .await
+    {
+      Ok(GetItemOutput { item: Some(_), .. }) => Ok(true),
+      Ok(_) => Ok(false),
+      Err(e) => Err(Error::AwsSdk(e.into())),
+    }
+  }
 }
 
 #[derive(
   Debug, derive_more::Display, derive_more::From, derive_more::Error,
 )]
 pub enum Error {
   #[display(...)]
   AwsSdk(DynamoDBError),
   #[display(...)]
   Attribute(DBItemError),
 }
 
 #[derive(Debug, derive_more::Error, derive_more::Constructor)]
 pub struct DBItemError {
   attribute_name: &'static str,
   attribute_value: Option<AttributeValue>,
   attribute_error: DBItemAttributeError,
 }
 
 impl Display for DBItemError {
   fn fmt(&self, f: &mut Formatter) -> FmtResult {
     match &self.attribute_error {
       DBItemAttributeError::Missing => {
         write!(f, "Attribute {} is missing", self.attribute_name)
       }
       DBItemAttributeError::IncorrectType => write!(
         f,
         "Value for attribute {} has incorrect type: {:?}",
         self.attribute_name, self.attribute_value
       ),
       error => write!(
         f,
         "Error regarding attribute {} with value {:?}: {}",
         self.attribute_name, self.attribute_value, error
       ),
     }
   }
 }
 
 #[derive(Debug, derive_more::Display, derive_more::Error)]
 pub enum DBItemAttributeError {
   #[display(...)]
   Missing,
   #[display(...)]
   IncorrectType,
   #[display(...)]
   InvalidTimestamp(chrono::ParseError),
   #[display(...)]
   Pake(ProtocolError),
 }
 
 type AttributeName = String;
 
 fn create_simple_primary_key(
   partition_key: (AttributeName, String),
 ) -> HashMap<AttributeName, AttributeValue> {
   HashMap::from([(partition_key.0, AttributeValue::S(partition_key.1))])
 }
 
 fn create_composite_primary_key(
   partition_key: (AttributeName, String),
   sort_key: (AttributeName, String),
 ) -> HashMap<AttributeName, AttributeValue> {
   let mut primary_key = create_simple_primary_key(partition_key);
   primary_key.insert(sort_key.0, AttributeValue::S(sort_key.1));
   primary_key
 }
 
 fn parse_created_attribute(
   attribute: Option<AttributeValue>,
 ) -> Result<DateTime<Utc>, DBItemError> {
   if let Some(AttributeValue::S(created)) = &attribute {
     created.parse().map_err(|e| {
       DBItemError::new(
         ACCESS_TOKEN_TABLE_CREATED_ATTRIBUTE,
         attribute,
         DBItemAttributeError::InvalidTimestamp(e),
       )
     })
   } else {
     Err(DBItemError::new(
       ACCESS_TOKEN_TABLE_CREATED_ATTRIBUTE,
       attribute,
       DBItemAttributeError::Missing,
     ))
   }
 }
 
 fn parse_auth_type_attribute(
   attribute: Option<AttributeValue>,
 ) -> Result<AuthType, DBItemError> {
   if let Some(AttributeValue::S(auth_type)) = &attribute {
     match auth_type.as_str() {
       "password" => Ok(AuthType::Password),
       "wallet" => Ok(AuthType::Wallet),
       _ => Err(DBItemError::new(
         ACCESS_TOKEN_TABLE_AUTH_TYPE_ATTRIBUTE,
         attribute,
         DBItemAttributeError::IncorrectType,
       )),
     }
   } else {
     Err(DBItemError::new(
       ACCESS_TOKEN_TABLE_AUTH_TYPE_ATTRIBUTE,
       attribute,
       DBItemAttributeError::Missing,
     ))
   }
 }
 
 fn parse_valid_attribute(
   attribute: Option<AttributeValue>,
 ) -> Result<bool, DBItemError> {
   match attribute {
     Some(AttributeValue::Bool(valid)) => Ok(valid),
     Some(_) => Err(DBItemError::new(
       ACCESS_TOKEN_TABLE_VALID_ATTRIBUTE,
       attribute,
       DBItemAttributeError::IncorrectType,
     )),
     None => Err(DBItemError::new(
       ACCESS_TOKEN_TABLE_VALID_ATTRIBUTE,
       attribute,
       DBItemAttributeError::Missing,
     )),
   }
 }
 
 fn parse_token_attribute(
   attribute: Option<AttributeValue>,
 ) -> Result<String, DBItemError> {
   match attribute {
     Some(AttributeValue::S(token)) => Ok(token),
     Some(_) => Err(DBItemError::new(
       ACCESS_TOKEN_TABLE_TOKEN_ATTRIBUTE,
       attribute,
       DBItemAttributeError::IncorrectType,
     )),
     None => Err(DBItemError::new(
       ACCESS_TOKEN_TABLE_TOKEN_ATTRIBUTE,
       attribute,
       DBItemAttributeError::Missing,
     )),
   }
 }
 
 fn parse_registration_data_attribute(
   attribute: Option<AttributeValue>,
 ) -> Result<Vec<u8>, DBItemError> {
   match attribute {
     Some(AttributeValue::B(server_registration_bytes)) => {
       Ok(server_registration_bytes.into_inner())
     }
     Some(_) => Err(DBItemError::new(
       USERS_TABLE_REGISTRATION_ATTRIBUTE,
       attribute,
       DBItemAttributeError::IncorrectType,
     )),
     None => Err(DBItemError::new(
       USERS_TABLE_REGISTRATION_ATTRIBUTE,
       attribute,
       DBItemAttributeError::Missing,
     )),
   }
 }
 
 fn parse_map_attribute(
   attribute_name: &'static str,
   attribute_value: Option<AttributeValue>,
 ) -> Result<HashMap<String, AttributeValue>, DBItemError> {
   match attribute_value {
     Some(AttributeValue::M(map)) => Ok(map),
     Some(_) => Err(DBItemError::new(
       attribute_name,
       attribute_value,
       DBItemAttributeError::IncorrectType,
     )),
     None => Err(DBItemError::new(
       attribute_name,
       attribute_value,
       DBItemAttributeError::Missing,
     )),
   }
 }
 
 fn parse_string_attribute(
   attribute_name: &'static str,
   attribute_value: Option<AttributeValue>,
 ) -> Result<String, DBItemError> {
   match attribute_value {
     Some(AttributeValue::S(value)) => Ok(value),
     Some(_) => Err(DBItemError::new(
       attribute_name,
       attribute_value,
       DBItemAttributeError::IncorrectType,
     )),
     None => Err(DBItemError::new(
       attribute_name,
       attribute_value,
       DBItemAttributeError::Missing,
     )),
   }
 }
 
 fn create_device_info(
   flattened_device_key_upload: FlattenedDeviceKeyUpload,
   social_proof: Option<String>,
 ) -> HashMap<String, AttributeValue> {
   let mut device_info = HashMap::from([
     (
       USERS_TABLE_DEVICES_MAP_DEVICE_TYPE_ATTRIBUTE_NAME.to_string(),
       AttributeValue::S(Device::Client.to_string()),
     ),
     (
       USERS_TABLE_DEVICES_MAP_KEY_PAYLOAD_ATTRIBUTE_NAME.to_string(),
       AttributeValue::S(flattened_device_key_upload.key_payload),
     ),
     (
       USERS_TABLE_DEVICES_MAP_KEY_PAYLOAD_SIGNATURE_ATTRIBUTE_NAME.to_string(),
       AttributeValue::S(flattened_device_key_upload.key_payload_signature),
     ),
     (
       USERS_TABLE_DEVICES_MAP_CONTENT_PREKEY_ATTRIBUTE_NAME.to_string(),
       AttributeValue::S(flattened_device_key_upload.content_prekey),
     ),
     (
       USERS_TABLE_DEVICES_MAP_CONTENT_PREKEY_SIGNATURE_ATTRIBUTE_NAME
         .to_string(),
       AttributeValue::S(flattened_device_key_upload.content_prekey_signature),
     ),
     (
       USERS_TABLE_DEVICES_MAP_CONTENT_ONETIME_KEYS_ATTRIBUTE_NAME.to_string(),
       AttributeValue::L(
         flattened_device_key_upload
           .content_onetime_keys
           .into_iter()
           .map(AttributeValue::S)
           .collect(),
       ),
     ),
     (
       USERS_TABLE_DEVICES_MAP_NOTIF_PREKEY_ATTRIBUTE_NAME.to_string(),
       AttributeValue::S(flattened_device_key_upload.notif_prekey),
     ),
     (
       USERS_TABLE_DEVICES_MAP_NOTIF_PREKEY_SIGNATURE_ATTRIBUTE_NAME.to_string(),
       AttributeValue::S(flattened_device_key_upload.notif_prekey_signature),
     ),
     (
       USERS_TABLE_DEVICES_MAP_NOTIF_ONETIME_KEYS_ATTRIBUTE_NAME.to_string(),
       AttributeValue::L(
         flattened_device_key_upload
           .notif_onetime_keys
           .into_iter()
           .map(AttributeValue::S)
           .collect(),
       ),
     ),
   ]);
 
   if let Some(social_proof) = social_proof {
     device_info.insert(
       USERS_TABLE_DEVICES_MAP_SOCIAL_PROOF_ATTRIBUTE_NAME.to_string(),
       AttributeValue::S(social_proof),
     );
   }
 
   device_info
 }
 
 #[cfg(test)]
 mod tests {
   use super::*;
 
   #[test]
   fn test_create_simple_primary_key() {
     let partition_key_name = "userID".to_string();
     let partition_key_value = "12345".to_string();
     let partition_key =
       (partition_key_name.clone(), partition_key_value.clone());
     let mut primary_key = create_simple_primary_key(partition_key);
     assert_eq!(primary_key.len(), 1);
     let attribute = primary_key.remove(&partition_key_name);
     assert!(attribute.is_some());
     assert_eq!(attribute, Some(AttributeValue::S(partition_key_value)));
   }
 
   #[test]
   fn test_create_composite_primary_key() {
     let partition_key_name = "userID".to_string();
     let partition_key_value = "12345".to_string();
     let partition_key =
       (partition_key_name.clone(), partition_key_value.clone());
     let sort_key_name = "deviceID".to_string();
     let sort_key_value = "54321".to_string();
     let sort_key = (sort_key_name.clone(), sort_key_value.clone());
     let mut primary_key = create_composite_primary_key(partition_key, sort_key);
     assert_eq!(primary_key.len(), 2);
     let partition_key_attribute = primary_key.remove(&partition_key_name);
     assert!(partition_key_attribute.is_some());
     assert_eq!(
       partition_key_attribute,
       Some(AttributeValue::S(partition_key_value))
     );
     let sort_key_attribute = primary_key.remove(&sort_key_name);
     assert!(sort_key_attribute.is_some());
     assert_eq!(sort_key_attribute, Some(AttributeValue::S(sort_key_value)))
   }
 
   #[test]
   fn validate_keys() {
     // Taken from test user
     let example_payload = r#"{\"notificationIdentityPublicKeys\":{\"curve25519\":\"DYmV8VdkjwG/VtC8C53morogNJhpTPT/4jzW0/cxzQo\",\"ed25519\":\"D0BV2Y7Qm36VUtjwyQTJJWYAycN7aMSJmhEsRJpW2mk\"},\"primaryIdentityPublicKeys\":{\"curve25519\":\"Y4ZIqzpE1nv83kKGfvFP6rifya0itRg2hifqYtsISnk\",\"ed25519\":\"cSlL+VLLJDgtKSPlIwoCZg0h0EmHlQoJC08uV/O+jvg\"}}"#;
     let serialized_payload = KeyPayload::from_str(&example_payload).unwrap();
 
     assert_eq!(
       serialized_payload
         .notification_identity_public_keys
         .curve25519,
       "DYmV8VdkjwG/VtC8C53morogNJhpTPT/4jzW0/cxzQo"
     );
   }
 }