diff --git a/backend/sync_lib/Cargo.toml b/backend/sync_lib/Cargo.toml
new file mode 100644
index 00000000..1e1b048a
--- /dev/null
+++ b/backend/sync_lib/Cargo.toml
@@ -0,0 +1,9 @@
+[package]
+name = "sync_lib"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+base64 = "0.22.1"
+
+thiserror = {workspace = true}
diff --git a/backend/sync_lib/src/errors.rs b/backend/sync_lib/src/errors.rs
new file mode 100644
index 00000000..acc865e1
--- /dev/null
+++ b/backend/sync_lib/src/errors.rs
@@ -0,0 +1,24 @@
+use base64::DecodeError;
+use thiserror::Error;
+
+#[derive(Error, Debug)]
+pub enum SyncLibError {
+    #[error("Base64 decoding error: {}", .reason)]
+    DecodingError { reason: String },
+}
+
+impl From<DecodeError> for SyncLibError {
+    fn from(e: DecodeError) -> Self {
+        SyncLibError::DecodingError {
+            reason: e.to_string(),
+        }
+    }
+}
+
+impl From<std::string::FromUtf8Error> for SyncLibError {
+    fn from(e: std::string::FromUtf8Error) -> Self {
+        SyncLibError::DecodingError {
+            reason: e.to_string(),
+        }
+    }
+}
diff --git a/backend/sync_lib/src/lib.rs b/backend/sync_lib/src/lib.rs
new file mode 100644
index 00000000..5e42e905
--- /dev/null
+++ b/backend/sync_lib/src/lib.rs
@@ -0,0 +1,25 @@
+use base64::{Engine as _, engine::general_purpose::STANDARD_NO_PAD};
+use errors::SyncLibError;
+
+pub mod errors;
+
+pub fn bytes_to_base64(input: &[u8]) -> String {
+    STANDARD_NO_PAD.encode(input)
+}
+
+pub fn string_to_base64(input: &str) -> String {
+    bytes_to_base64(input.as_bytes())
+}
+
+pub fn base64_to_bytes(input: &str) -> Result<Vec<u8>, SyncLibError> {
+    STANDARD_NO_PAD.decode(input).map_err(SyncLibError::from)
+}
+
+pub fn base64_to_string(input: &str) -> Result<String, SyncLibError> {
+    let bytes = base64_to_bytes(input)?;
+    String::from_utf8(bytes).map_err(SyncLibError::from)
+}
+
+pub fn is_binary(data: &[u8]) -> bool {
+    data.iter().any(|&b| b == 0)
+}