5G • Security
COUNT Parameter
32-Bit Cryptographic COUNT Value
32-bit integer constructed from hyper-frame number and sequence number acting as IV for encryption ciphers.
Technical Explanation
The COUNT value prevents keystream reuse in stream ciphers. In PDCP, COUNT is formed by concatenating the Hyper Frame Number (HFN, upper bits) with the PDCP Sequence Number (lower bits). In NAS, COUNT is incremented per NAS PDU. It serves as an initialization vector ensuring identical plaintext yields different ciphertext.
Key Functions
- 32-bit monotonically incrementing counter acting as cryptographic IV
- Combines Hyper Frame Number (HFN) with packet Sequence Number
- Guarantees keystream freshness, preventing cipher state recovery attacks
Specifications
3GPP TS 33.501, TS 38.323
Interfaces
UuN1
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