diff --git a/src/error.rs b/src/error.rs
index ee413dd..1180295 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -1,3 +1,5 @@
+use crate::ikm::IkmId;
+
 pub(crate) type Result<T, E = Error> = core::result::Result<T, E>;
 
 #[derive(thiserror::Error, Debug)]
@@ -7,7 +9,7 @@ pub enum Error {
 	#[error("ikm error: no input key material available")]
 	IkmNoneAvailable,
 	#[error("ikm error: {0}: input key material not found")]
-	IkmNotFound(u32),
+	IkmNotFound(IkmId),
 	#[error("parsing error: invalid base64-urlsafe-nopadding data: {0}")]
 	ParsingBase64Error(base64ct::Error),
 	#[error("parsing error: encoded data: invalid IKM id: {0:?}")]
diff --git a/src/ikm.rs b/src/ikm.rs
index 2ecd9ff..080fb70 100644
--- a/src/ikm.rs
+++ b/src/ikm.rs
@@ -6,9 +6,11 @@ use std::time::{Duration, SystemTime};
 const IKM_STRUCT_SIZE: usize = 57;
 const IKM_CONTENT_SIZE: usize = 32;
 
+pub(crate) type IkmId = u32;
+
 #[derive(Debug)]
 pub(crate) struct InputKeyMaterial {
-	pub(crate) id: u32,
+	pub(crate) id: IkmId,
 	pub(crate) scheme: Scheme,
 	pub(crate) content: [u8; IKM_CONTENT_SIZE],
 	pub(crate) created_at: SystemTime,
@@ -43,7 +45,7 @@ impl InputKeyMaterial {
 
 	pub(crate) fn from_bytes(b: [u8; IKM_STRUCT_SIZE]) -> Result<Self> {
 		Ok(Self {
-			id: u32::from_le_bytes(b[0..4].try_into().unwrap()),
+			id: IkmId::from_le_bytes(b[0..4].try_into().unwrap()),
 			scheme: u32::from_le_bytes(b[4..8].try_into().unwrap()).try_into()?,
 			content: b[8..40].try_into().unwrap(),
 			created_at: InputKeyMaterial::bytes_to_system_time(&b[40..48])?,
@@ -131,7 +133,7 @@ impl InputKeyMaterialList {
 	}
 
 	#[cfg(feature = "encryption")]
-	pub(crate) fn get_ikm_by_id(&self, id: u32) -> Result<&InputKeyMaterial> {
+	pub(crate) fn get_ikm_by_id(&self, id: IkmId) -> Result<&InputKeyMaterial> {
 		self.ikm_lst
 			.iter()
 			.find(|&ikm| ikm.id == id)
diff --git a/src/storage.rs b/src/storage.rs
index 3fb9bcb..9b2f69a 100644
--- a/src/storage.rs
+++ b/src/storage.rs
@@ -1,5 +1,6 @@
 use crate::encryption::EncryptedData;
 use crate::error::{Error, Result};
+use crate::ikm::IkmId;
 use base64ct::{Base64UrlUnpadded, Encoding};
 
 const STORAGE_SEPARATOR: &str = ":";
@@ -15,7 +16,7 @@ fn decode_data(s: &str) -> Result<Vec<u8>> {
 	Ok(Base64UrlUnpadded::decode_vec(s)?)
 }
 
-pub(crate) fn encode(ikm_id: u32, encrypted_data: &EncryptedData) -> String {
+pub(crate) fn encode(ikm_id: IkmId, encrypted_data: &EncryptedData) -> String {
 	let mut ret = String::new();
 	ret += &encode_data(&ikm_id.to_le_bytes());
 	ret += STORAGE_SEPARATOR;
@@ -25,7 +26,7 @@ pub(crate) fn encode(ikm_id: u32, encrypted_data: &EncryptedData) -> String {
 	ret
 }
 
-pub(crate) fn decode(data: &str) -> Result<(u32, EncryptedData)> {
+pub(crate) fn decode(data: &str) -> Result<(IkmId, EncryptedData)> {
 	let v: Vec<&str> = data.split(STORAGE_SEPARATOR).collect();
 	if v.len() != NB_PARTS {
 		return Err(Error::ParsingEncodedDataInvalidPartLen(NB_PARTS, v.len()));
@@ -35,7 +36,7 @@ pub(crate) fn decode(data: &str) -> Result<(u32, EncryptedData)> {
 		.clone()
 		.try_into()
 		.map_err(|_| Error::ParsingEncodedDataInvalidIkmId(id_raw))?;
-	let id = u32::from_le_bytes(id_raw);
+	let id = IkmId::from_le_bytes(id_raw);
 	let encrypted_data = EncryptedData {
 		nonce: decode_data(v[1])?,
 		ciphertext: decode_data(v[2])?,
@@ -45,10 +46,11 @@ pub(crate) fn decode(data: &str) -> Result<(u32, EncryptedData)> {
 
 #[cfg(test)]
 mod tests {
+	use crate::ikm::IkmId;
 	use crate::storage::EncryptedData;
 
 	const TEST_STR: &str = "KgAAAA:a5SpjAoqhvuI9n3GPhDKuotqoLbf7_Fb:TI24Wr_g-ZV7_X1oHqVKak9iRlQSneYVOMWB-3Lp-hFHKfxfnY-zR_bN";
-	const TEST_IKM_ID: u32 = 42;
+	const TEST_IKM_ID: IkmId = 42;
 	const TEST_NONCE: &'static [u8] = &[
 		0x6b, 0x94, 0xa9, 0x8c, 0x0a, 0x2a, 0x86, 0xfb, 0x88, 0xf6, 0x7d, 0xc6, 0x3e, 0x10, 0xca,
 		0xba, 0x8b, 0x6a, 0xa0, 0xb6, 0xdf, 0xef, 0xf1, 0x5b,