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FULLY HOMOMORPHIC ENCRYPTION WITH POLYLOG OVERHEAD

FULLY HOMOMORPHIC ENCRYPTION WITH POLYLOG OVERHEAD

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Handling Large Permutations<br />

• Can we arbitrarily permute m×ℓ items, given in m<br />

arrays of size ℓ, using ℓ-ADD, ℓ-MUL, ℓ-PERMUTE?<br />

•<br />

• Theorem (Lev, Pippenger, Valiant ‘84): A permutation<br />

π over m×ℓ addresses (viewed as a rectangle) can be<br />

decomposed as π = π3◦ π 2◦ π 1, where:<br />

• π 1 only permutes within the columns<br />

• π 2 only permutes within the rows<br />

• π3 only permutes within the columns<br />

• Within rows: Use ℓ-PERMUTE on each row (array).<br />

• Within columns: swap elements with same index<br />

using ℓ-SELECT.

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