[Resource Topic] 2002/148: The EMD Mode of Operation (A Tweaked, Wide-Blocksize, Strong PRP)

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The EMD Mode of Operation (A Tweaked, Wide-Blocksize, Strong PRP)

Authors: Phillip Rogaway


We describe a block-cipher mode of operation, EMD,
that builds a strong pseudorandom permutation (PRP)
on nm bits (m\ge2) out of
a strong PRP on n bits (i.e., a block cipher).
The constructed PRP is also tweaked
(in the sense of [LRW02]):
to determine the nm-bit ciphertext block C=\E_K^T(P)
one provides, besides the key K and the nm-bit plaintext block P, an n-bit tweak T.
The mode uses 2m block-cipher calls and
no other complex or computationally expensive steps
(such as universal hashing).
Encryption and decryption are identical except that encryption uses the
forward direction of the underlying block cipher and decryption uses the backwards
We suggest that EMD provides an attractive solution to the
disk-sector encryption problem, where one wants to encipher
the contents of an nm-bit disk sector in a way that
depends on the sector index and is secure against
chosen-plaintext/chosen-ciphertext attack.

ePrint: https://eprint.iacr.org/2002/148

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