diff --git a/acme_common/src/error.rs b/acme_common/src/error.rs
index 3ab32eb..c0699f4 100644
--- a/acme_common/src/error.rs
+++ b/acme_common/src/error.rs
@@ -69,6 +69,12 @@ impl From<std::time::SystemTimeError> for Error {
     }
 }
 
+impl From<base64::DecodeError> for Error {
+    fn from(error: base64::DecodeError) -> Self {
+        format!("base 64 decode error: {}", error).into()
+    }
+}
+
 impl From<syslog::Error> for Error {
     fn from(error: syslog::Error) -> Self {
         format!("syslog error: {}", error).into()
diff --git a/acme_common/src/lib.rs b/acme_common/src/lib.rs
index d81b884..657f621 100644
--- a/acme_common/src/lib.rs
+++ b/acme_common/src/lib.rs
@@ -42,6 +42,11 @@ pub fn b64_encode<T: ?Sized + AsRef<[u8]>>(input: &T) -> String {
     base64::encode_config(input, base64::URL_SAFE_NO_PAD)
 }
 
+pub fn b64_decode<T: ?Sized + AsRef<[u8]>>(input: &T) -> Result<Vec<u8>, error::Error> {
+    let res = base64::decode_config(input, base64::URL_SAFE_NO_PAD)?;
+    Ok(res)
+}
+
 pub fn init_server(foreground: bool, pid_file: Option<&str>, default_pid_file: &str) {
     if !foreground {
         let daemonize = Daemonize::new().pid_file(pid_file.unwrap_or(default_pid_file));