diff --git a/backend/src/errors.rs b/backend/src/errors.rs
index fde8436..77c6a30 100644
--- a/backend/src/errors.rs
+++ b/backend/src/errors.rs
@@ -56,6 +56,10 @@ pub enum SpecialErrors {
     MissingFile,
     #[error("User email rejected: domain not allowed")]
     UnallowedDomain,
+    #[error("The primary key or a subkey does not expire")]
+    KeyNonExpiring,
+    #[error("The primary keys or a subkeys validity is too long")]
+    KeyValidityTooLong,
 }
 
 #[derive(Debug)]
@@ -104,6 +108,8 @@ impl ResponseError for CompatErr {
                 SpecialErrors::MalformedEmail => StatusCode::BAD_REQUEST,
                 SpecialErrors::MissingFile => StatusCode::NOT_FOUND,
                 SpecialErrors::UnallowedDomain => StatusCode::UNAUTHORIZED,
+                SpecialErrors::KeyNonExpiring => StatusCode::BAD_REQUEST,
+                SpecialErrors::KeyValidityTooLong => StatusCode::BAD_REQUEST,
             },
         }
     }
diff --git a/backend/src/settings.rs b/backend/src/settings.rs
index db23705..3b330f1 100644
--- a/backend/src/settings.rs
+++ b/backend/src/settings.rs
@@ -18,6 +18,7 @@ pub struct Settings {
     pub bind_host: String,
     pub external_url: Url,
     pub mail_settings: MailSettings,
+    pub policy: Option<Policy>,
 }
 
 #[derive(Serialize, Deserialize, Debug)]
@@ -31,6 +32,11 @@ pub struct MailSettings {
     pub mail_subject: String,
 }
 
+#[derive(Serialize, Deserialize, Debug)]
+pub struct Policy {
+    pub key_max_validity: Option<u64>,
+}
+
 #[derive(Serialize, Deserialize, Debug)]
 pub enum Variant {
     Advanced,
diff --git a/backend/src/utils.rs b/backend/src/utils.rs
index b07a8ca..9a8f94e 100644
--- a/backend/src/utils.rs
+++ b/backend/src/utils.rs
@@ -22,13 +22,36 @@ use sequoia_openpgp::{parse::Parse, Cert};
 use std::{
     fs,
     path::{Path, PathBuf},
+    time::Duration,
 };
 
 pub fn validate_cert(cert: &Cert) -> Result<ValidCert> {
-    match log_err!(cert.with_policy(crate::settings::POLICY, None), debug) {
-        Ok(validcert) => Ok(validcert),
+    let validcert = match log_err!(cert.with_policy(crate::settings::POLICY, None), debug) {
+        Ok(validcert) => validcert,
         Err(_) => Err(SpecialErrors::InvalidCert)?,
+    };
+
+    if let Some(policy_settings) = &SETTINGS.policy {
+        if let Some(max_validity_setting) = policy_settings.key_max_validity {
+            let max_validity = Duration::from_secs(max_validity_setting);
+
+            if !max_validity.is_zero() {
+                for key in validcert.keys() {
+                    let validity = key.key_validity_period();
+
+                    if validity.is_none() {
+                        debug!("Certificate was rejected: The primary key or a subkey has validity period of zero");
+                        return Err(SpecialErrors::KeyNonExpiring)?
+                    } else if validity > Some(max_validity) {
+                        debug!("Certificate was rejected: The primary key or a subkey has a validity period greater than {max_validity_setting} seconds");
+                        return Err(SpecialErrors::KeyValidityTooLong)?
+                    }
+                }
+            }
+        }
     }
+
+    Ok(validcert)
 }
 
 pub fn encode_local(local: &str) -> String {