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TSG SA WG3 #7, The Hague, 26-27 October, 1999 S3-99384
DRAFT 3G CHANGE REQUEST
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Please see embedded help file at the bottom of this
page for instructions on how to fill in this form correctly.
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TS 33.105
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CR
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004
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Current Version:
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V3.1.0
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3G specification number
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CR number as allocated by 3G support team
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For submission to TSG
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SA#6
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for approval
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x
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(only one box should
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list TSG meeting no. here
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for information
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be marked with an X)
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Form: 3G CR cover sheet, version 1.0 The latest version of this form is available from: ftp://ftp.3gpp.org/Information/3GCRF-xx.rtf
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Proposed change affects:
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USIM
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ME
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X
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UTRAN
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X
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Core Network
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(at least one should be marked with an X)
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Source:
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TSG SA WG3
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Date:
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99-10-27
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Subject:
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Time variant parameter for synchronisation of ciphering
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3G Work item:
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Security
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Category:
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F Correction
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A Corresponds to a correction in a 2G specification
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(only one category
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B Addition of feature
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shall be marked
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C Functional modification of feature
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with an X)
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D Editorial modification
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X
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Reason for
change:
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On the algorithms for both data confidentiality and data integrity, one of input parameters is COUNT, a time variant parameter for synchronisation. Due to progress in TSG S3, it is better to use a time variant parameter separately in order to improve security. A time variant parameter used for ciphering is renamed COUNT-C.
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Clauses affected:
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3.3, 5.2.1, 5.2.7.2
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Other specs
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Other 3G core specifications
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List of CRs:
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affected:
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Other 2G core specifications
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List of CRs:
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MS test specifications
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List of CRs:
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BSS test specifications
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List of CRs:
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O&M specifications
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List of CRs:
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Other
comments:
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3.3 Abbreviations
For the purposes of the present document, the following abbreviations apply:
3GPP 3rd Generation Partnership Project
AK Anonymity key
AuC Authentication Centre
AUTN Authentication token
CK Cipher key
COUNT-C Time variant parameter for synchronisation of ciphering
COUNT-I Time variant parameter for synchronisation of data integrity
EMUI Encrypted Mobile User Identity
GK User group key
IK Integrity key
IMUI International Mobile User Identity
IPR Intellectual Property Right
MAC Medium access control (sublayer of Layer 2 in RAN)
MAC Message authentication code
MAC-A MAC used for authentication and key agreement
MAC-I MAC used for data integrity of signalling messages
PDU Protocol data unit
RAND Random challenge
RES User response
RLC Radio link control (sublayer of Layer 2 in RAN)
RNC Radio network controller
SEQ_UIC Sequence for user identity confidentiality
SDU Signalling data unit
SQN Sequence number
UE User equipment
USIM User Services Identity Module
XMAC-A Expected MAC used for authentication and key agreement
XMAC-I Expected MAC used for data integrity of signalling messages
XRES Expected user response
5.2.1 Overview
The mechanism for data confidentiality of user data and signalling data that is described in 6.4 of [1] requires the following cryptographic function:
f8 UMTS encryption algorithm.
Figure 2 illustrates the use of f8 to encrypt plaintext by applying a keystream using a bitwise XOR operation. The plaintext may be recovered by generating the same keystream using the same input parameters and applying it to the ciphertext using a bitwise XOR operation.
Figure 2: Ciphering user and signalling data transmitted over the radio access link
The input parameters to the algorithm are the Cipher Key (CK), a time dependent input (COUNT-C), the bearer identity (BEARER), the direction of transmission (DIRECTION) and the length of the keystream required (LENGTH). Based on these input parameters the algorithm generates the output keystream block (KEYSTREAM) which is used to encrypt the input plaintext block (PLAINTEXT) to produce the output ciphertext block (CIPHERTEXT).
The input parameter LENGTH shall affect only the length of the KEYSTREAM BLOCK, not the actual bits in it.
5.2.7.2 COUNT-C
COUNT-C: a time dependent input.
COUNT-C[0], COUNT-C[1], …, COUNT-C[31]
The length of the COUNT-C parameter is 32 bits. It is assumed that sychronisation of the keystream will be based on the use of a physical layer (Layer 1) frame counter combined with a hyperframe counter introduced to avoid re-use of the keystream. This allows the keystream to be synchronised every 10ms physical layer frame. The exact structure of the COUNT-C parameter cannot be specified at present. However, it is assumed to be a 32 bit counter.
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