Padding in 128 EIA-3

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Padding in 128 EIA-3

Post  zeshan on Thu Feb 03, 2011 9:42 pm

Hi,

My queries regarding padding of 128-EIA3 are as follows:-

1. Is Padding a bit 1 is necessary in 128-EIA3 as it is mentioned in document 4 but document 1 has no in formation regarding it.

2.What is the cryptographic importance of a Padding a bit 1.

3.What is the value of padded bit either 0 or 1.

4.Is length of padded bit is included in variable LENGTH or it is just an extra bit.

Regards

zeshan

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Re: Padding in 128 EIA-3

Post  Peng Wang on Mon Feb 07, 2011 3:47 pm

>1. Is Padding a bit 1 is necessary in 128-EIA3 as it is mentioned in document 4 but document 1 has no in formation regarding it.

Yes, it is necessary in 128-EIA3. The core of 128-EIA3 is a univesal hash funtion and the padding is a part of the universal hash function. The MAC value is generated by one-time-pad masking of the univeral hashing value. The descryption of document 4 and document 1 is not consistent.


>2.What is the cryptographic importance of a Padding a bit 1.

Without padding, the uinversal hash function is not AXU (Almost XOR Universal) and can not handle variable-input-length messages.

>3.What is the value of padded bit either 0 or 1.

The Padding bit is 1 for any message.

>4.Is length of padded bit is included in variable LENGTH or it is just an extra bit.

Extra bit.

PS.
Since a bad mask was used in the former version of 128-EIA3 and a forgery attack was presented by Thomas Fuhr et al [FGRV10], a minor modification was made in the newest version of 128-EIA3.

[FGRV10] Thomas Fuhr, Henri Gilbert, Jean-René Reinhard, and Marion Videau, A forgery attack on the candidate LTE integrity algorithm 128-EIA3, http://eprint.iacr.org/2010/618.

Peng Wang

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