skinny

Construction

Number of rounds for SKINNY-n-t, with n-bit internal state and t-bit tweakey state.

	Tweakey Size t
Block Size n	n	2n	3n
64	32	36	40
128	40	48	56

The SKINNY round function applies five different transformations: SubCells (SC), AddConstants (AC), AddRoundTweakey (ART), ShiftRows (SR) and MixColumns (MC).

• Tweakey Schedule
  • Permutation
  • LFSR
• SubCells (SC): Depending on the block size, a 4-bit Sbox (for 64-bit block) or a 8-bit Sbox (for 128-bit block) is used.
• AddConstants (AC): Some round-dependent constants are XORed to the first nibbles/bytes column of the cipher internal state.
• AddRoundTweakey (ART): Half a block is extracted from the tweakey state and XORed to the cipher internal state. The tweakey nibbles/bytes are permuted and updated with simple LFSRs.
• ShiftRows (SR): The nibbles/bytes of the cipher internal state are rotated to the right row-wise by some specified number of positions.
• MixColumns (MC): Each nibbles/bytes column of the cipher internal state are multiplied by a binary matrix.

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