Tools / Telecom & Networks
NAS Message Decoder (4G/5G)
Paste a NAS PDU hex string to identify the protocol (EMM/ESM/5GMM/5GSM), security header type, and message type name — covering 4G EPS (TS 24.301) and 5G NAS (TS 24.501). Not a full ASN.1 decoder.
Free
Scope: This tool identifies the NAS message type, protocol discriminator, and security header from the first bytes of a raw NAS PDU. It is NOT a full ASN.1/IE-level NAS decoder. For ciphered messages, the inner message type is after the MAC + sequence number fields and cannot be decoded without NAS keys. Covers 4G EPS NAS (TS 24.301: EMM/ESM) and 5G NAS (TS 24.501: 5GMM/5GSM).
Paste hex — tolerates spaces, 0x prefixes, newlines, and dashes. Example: 7E 00 41
Load example:
Paste a NAS PDU hex string above or click an example to decode it.
Protocol reference — supported PD / EPD values
| Byte 0 value | Protocol | Standard | Examples |
|---|---|---|---|
| 0x7E | 5GMM | TS 24.501 §9.7.1 | Registration request (0x41), Auth request (0x56), SMC (0x5D) |
| 0x2E | 5GSM | TS 24.501 §9.7.2 | PDU session establishment request (0xC1) |
| 0x07 / 0x_7 | EMM (4G) | TS 24.301 §9.8.1 | Attach request (0x41), TAU request (0x48), SMC (0x5D) |
| 0x02 / 0x_2 | ESM (4G) | TS 24.301 §9.8.2 | PDN connectivity request (0xD0) |