diff --git a/rs-matter/src/cert/asn1_writer.rs b/rs-matter/src/cert/asn1_writer.rs
index 87fac3c..7eb1c96 100644
--- a/rs-matter/src/cert/asn1_writer.rs
+++ b/rs-matter/src/cert/asn1_writer.rs
@@ -264,8 +264,8 @@ impl<'a> CertConsumer for ASN1Writer<'a> {
         self.write_str(0x06, oid)
     }
 
-    fn utctime(&mut self, _tag: &str, epoch: u32) -> Result<(), Error> {
-        let matter_epoch = MATTER_EPOCH_SECS + epoch as u64;
+    fn utctime(&mut self, _tag: &str, epoch: u64) -> Result<(), Error> {
+        let matter_epoch = MATTER_EPOCH_SECS + epoch;
 
         let dt = OffsetDateTime::from_unix_timestamp(matter_epoch as _).unwrap();
 
diff --git a/rs-matter/src/cert/mod.rs b/rs-matter/src/cert/mod.rs
index 8878622..9e03a52 100644
--- a/rs-matter/src/cert/mod.rs
+++ b/rs-matter/src/cert/mod.rs
@@ -21,7 +21,7 @@ use crate::{
     crypto::KeyPair,
     error::{Error, ErrorCode},
     tlv::{self, FromTLV, OctetStr, TLVArray, TLVElement, TLVWriter, TagType, ToTLV},
-    utils::writebuf::WriteBuf,
+    utils::{epoch::MATTER_CERT_DOESNT_EXPIRE, writebuf::WriteBuf},
 };
 use log::error;
 use num_derive::FromPrimitive;
@@ -650,8 +650,14 @@ impl<'a> Cert<'a> {
         self.issuer.encode("Issuer:", w)?;
 
         w.start_seq("Validity:")?;
-        w.utctime("Not Before:", self.not_before)?;
-        w.utctime("Not After:", self.not_after)?;
+        w.utctime("Not Before:", self.not_before.into())?;
+        if self.not_after == 0 {
+            // As per the spec a Not-After value of 0, indicates no well-defined
+            // expiration date and should return in GeneralizedTime of 99991231235959Z
+            w.utctime("Not After:", MATTER_CERT_DOESNT_EXPIRE)?;
+        } else {
+            w.utctime("Not After:", self.not_after.into())?;
+        }
         w.end_seq()?;
 
         self.subject.encode("Subject:", w)?;
@@ -710,8 +716,9 @@ impl<'a> CertVerifier<'a> {
         let k = KeyPair::new_from_public(parent.get_pubkey())?;
         k.verify_msg(asn1, self.cert.get_signature()).map_err(|e| {
             error!(
-                "Error in signature verification of certificate: {:x?}",
-                self.cert.get_subject_key_id()
+                "Error in signature verification of certificate: {:x?} by {:x?}",
+                self.cert.get_subject_key_id(),
+                parent.get_subject_key_id()
             );
             e
         })?;
@@ -744,7 +751,7 @@ pub trait CertConsumer {
     fn start_ctx(&mut self, tag: &str, id: u8) -> Result<(), Error>;
     fn end_ctx(&mut self) -> Result<(), Error>;
     fn oid(&mut self, tag: &str, oid: &[u8]) -> Result<(), Error>;
-    fn utctime(&mut self, tag: &str, epoch: u32) -> Result<(), Error>;
+    fn utctime(&mut self, tag: &str, epoch: u64) -> Result<(), Error>;
 }
 
 const MAX_DEPTH: usize = 10;
@@ -826,6 +833,16 @@ mod tests {
         );
     }
 
+    #[test]
+    fn test_zero_value_of_not_after_field() {
+        let noc = Cert::new(&test_vectors::NOC_NOT_AFTER_ZERO).unwrap();
+        let rca = Cert::new(&test_vectors::RCA_FOR_NOC_NOT_AFTER_ZERO).unwrap();
+
+        let v = noc.verify_chain_start();
+        let v = v.add_cert(&rca).unwrap();
+        v.finalise().unwrap();
+    }
+
     #[test]
     fn test_cert_corrupted() {
         use crate::error::ErrorCode;
@@ -1112,5 +1129,47 @@ mod tests {
             0x16, 0x80, 0x14, 0x72, 0xc2, 0x01, 0xf7, 0x57, 0x19, 0x13, 0xb3, 0x48, 0xca, 0x00,
             0xca, 0x7b, 0x45, 0xf4, 0x77, 0x46, 0x68, 0xc9, 0x7e,
         ];
+
+        /// An NOC that contains a Not-After validity field of '0'
+        pub const NOC_NOT_AFTER_ZERO: [u8; 251] = [
+            0x15, 0x30, 0x1, 0x1, 0x1, 0x24, 0x2, 0x1, 0x37, 0x3, 0x27, 0x14, 0xfc, 0x8d, 0xcf,
+            0x45, 0x19, 0xff, 0x9a, 0x9a, 0x24, 0x15, 0x1, 0x18, 0x26, 0x4, 0x21, 0x39, 0x5a, 0x2c,
+            0x24, 0x5, 0x0, 0x37, 0x6, 0x24, 0x15, 0x1, 0x26, 0x11, 0x6c, 0x4a, 0x95, 0xd2, 0x18,
+            0x24, 0x7, 0x1, 0x24, 0x8, 0x1, 0x30, 0x9, 0x41, 0x4, 0x41, 0x7f, 0xb1, 0x61, 0xb0,
+            0xbe, 0x19, 0x41, 0x81, 0xb9, 0x9f, 0xe8, 0x7b, 0xdd, 0xdf, 0xc4, 0x46, 0xe0, 0x74,
+            0xba, 0x83, 0x21, 0xda, 0x3d, 0xf7, 0x88, 0x68, 0x14, 0xa6, 0x9d, 0xa9, 0x14, 0x88,
+            0x94, 0x1e, 0xd3, 0x86, 0x62, 0xc7, 0x6f, 0xb4, 0x79, 0xd2, 0xaf, 0x34, 0xe7, 0xd6,
+            0x4d, 0x87, 0x29, 0x67, 0x10, 0x73, 0xb9, 0x81, 0xe0, 0x9, 0xe1, 0x13, 0xbb, 0x6a,
+            0xd2, 0x21, 0xaa, 0x37, 0xa, 0x35, 0x1, 0x28, 0x1, 0x18, 0x24, 0x2, 0x1, 0x36, 0x3,
+            0x4, 0x2, 0x4, 0x1, 0x18, 0x30, 0x4, 0x14, 0x98, 0xaf, 0xa1, 0x3d, 0x41, 0x67, 0x7a,
+            0x34, 0x8c, 0x67, 0x6c, 0xcc, 0x17, 0x6e, 0xd5, 0x58, 0xd8, 0x2b, 0x86, 0x8, 0x30, 0x5,
+            0x14, 0xf8, 0xcf, 0xd0, 0x45, 0x6b, 0xe, 0xd1, 0x6f, 0xc5, 0x67, 0xdf, 0x81, 0xd7,
+            0xe9, 0xb7, 0xeb, 0x39, 0x78, 0xec, 0x40, 0x18, 0x30, 0xb, 0x40, 0xf9, 0x80, 0x94,
+            0xbf, 0xcf, 0x72, 0xa5, 0x54, 0x87, 0x12, 0x35, 0xc, 0x38, 0x79, 0xa8, 0xb, 0x21, 0x94,
+            0xb5, 0x71, 0x2, 0xcb, 0xb, 0xda, 0xf9, 0x6c, 0x54, 0xcb, 0x50, 0x4b, 0x2, 0x5, 0xea,
+            0xff, 0xfd, 0xb2, 0x1b, 0x24, 0x30, 0x79, 0xb1, 0x69, 0x87, 0xa5, 0x7, 0xc6, 0x76,
+            0x15, 0x70, 0xc0, 0xec, 0x14, 0xd3, 0x9f, 0x1a, 0xa7, 0xe1, 0xca, 0x25, 0x2e, 0x44,
+            0xfc, 0x96, 0x4d, 0x18,
+        ];
+        pub const RCA_FOR_NOC_NOT_AFTER_ZERO: [u8; 251] = [
+            0x15, 0x30, 0x1, 0x1, 0x0, 0x24, 0x2, 0x1, 0x37, 0x3, 0x27, 0x14, 0xfc, 0x8d, 0xcf,
+            0x45, 0x19, 0xff, 0x9a, 0x9a, 0x24, 0x15, 0x1, 0x18, 0x26, 0x4, 0xb1, 0x2a, 0x38, 0x2c,
+            0x26, 0x5, 0x31, 0x5e, 0x19, 0x2e, 0x37, 0x6, 0x27, 0x14, 0xfc, 0x8d, 0xcf, 0x45, 0x19,
+            0xff, 0x9a, 0x9a, 0x24, 0x15, 0x1, 0x18, 0x24, 0x7, 0x1, 0x24, 0x8, 0x1, 0x30, 0x9,
+            0x41, 0x4, 0x15, 0x69, 0x1e, 0x7b, 0x6a, 0xea, 0x5, 0xdb, 0xf8, 0x4b, 0xfd, 0xdc, 0x6c,
+            0x75, 0x46, 0x74, 0xb0, 0x60, 0xdb, 0x4, 0x71, 0xb6, 0xd0, 0x52, 0xf2, 0xf8, 0xe6,
+            0xbb, 0xd, 0xe5, 0x60, 0x1f, 0x84, 0x66, 0x4f, 0x3c, 0x90, 0x89, 0xa6, 0xc6, 0x99,
+            0x61, 0xfb, 0x89, 0xf7, 0xa, 0xa6, 0xe4, 0xa2, 0x21, 0xd3, 0x37, 0x30, 0x1b, 0xd2,
+            0x11, 0xc5, 0xcc, 0x0, 0xf4, 0x7a, 0x14, 0xfc, 0x3c, 0x37, 0xa, 0x35, 0x1, 0x29, 0x1,
+            0x18, 0x24, 0x2, 0x60, 0x30, 0x4, 0x14, 0xf8, 0xcf, 0xd0, 0x45, 0x6b, 0xe, 0xd1, 0x6f,
+            0xc5, 0x67, 0xdf, 0x81, 0xd7, 0xe9, 0xb7, 0xeb, 0x39, 0x78, 0xec, 0x40, 0x30, 0x5,
+            0x14, 0xf8, 0xcf, 0xd0, 0x45, 0x6b, 0xe, 0xd1, 0x6f, 0xc5, 0x67, 0xdf, 0x81, 0xd7,
+            0xe9, 0xb7, 0xeb, 0x39, 0x78, 0xec, 0x40, 0x18, 0x30, 0xb, 0x40, 0x4c, 0xae, 0xac,
+            0xc1, 0x26, 0xdd, 0x56, 0xc, 0x85, 0x86, 0xbc, 0xeb, 0xa2, 0xb5, 0xb7, 0xdf, 0x49,
+            0x92, 0x62, 0xcd, 0x2a, 0xb6, 0x4e, 0xc5, 0x31, 0x7c, 0xd9, 0xb, 0x1c, 0xe9, 0x6e,
+            0xe5, 0x82, 0xc7, 0xb8, 0xda, 0x22, 0x31, 0x7b, 0x23, 0x5a, 0x2a, 0xe6, 0x76, 0x28,
+            0xb6, 0xd4, 0xc7, 0x7b, 0x1c, 0x9c, 0x85, 0x71, 0x5f, 0xe6, 0xf6, 0x21, 0x50, 0x5c,
+            0xa7, 0x7c, 0xc7, 0x1d, 0x9a, 0x18,
+        ];
     }
 }
diff --git a/rs-matter/src/cert/printer.rs b/rs-matter/src/cert/printer.rs
index a4c4efe..b037576 100644
--- a/rs-matter/src/cert/printer.rs
+++ b/rs-matter/src/cert/printer.rs
@@ -122,8 +122,8 @@ impl<'a, 'b> CertConsumer for CertPrinter<'a, 'b> {
         }
         Ok(())
     }
-    fn utctime(&mut self, tag: &str, epoch: u32) -> Result<(), Error> {
-        let matter_epoch = MATTER_EPOCH_SECS + epoch as u64;
+    fn utctime(&mut self, tag: &str, epoch: u64) -> Result<(), Error> {
+        let matter_epoch = MATTER_EPOCH_SECS + epoch;
 
         let dt = OffsetDateTime::from_unix_timestamp(matter_epoch as _).unwrap();
 
diff --git a/rs-matter/src/utils/epoch.rs b/rs-matter/src/utils/epoch.rs
index 8236813..630f878 100644
--- a/rs-matter/src/utils/epoch.rs
+++ b/rs-matter/src/utils/epoch.rs
@@ -2,6 +2,11 @@ use core::time::Duration;
 
 pub type Epoch = fn() -> Duration;
 
+// As per the spec, if Not After is 0, it should set the time to GeneralizedTime value of
+// 99991231235959Z
+// So CERT_DOESNT_EXPIRE value is calculated as epoch(99991231235959Z) - MATTER_EPOCH_SECS
+pub const MATTER_CERT_DOESNT_EXPIRE: u64 = 252455615999;
+
 pub const MATTER_EPOCH_SECS: u64 = 946684800; // Seconds from 1970/01/01 00:00:00 till 2000/01/01 00:00:00 UTC
 
 pub fn dummy_epoch() -> Duration {