US 12,445,418 B2
Affine masking for secure encryption schemes
James Howe, Oxford (GB)
Assigned to PQShield Ltd, Oxford (GB)
Filed by PQShield Ltd, Oxford (GB)
Filed on Nov. 28, 2022, as Appl. No. 18/059,027.
Application 18/059,027 is a continuation of application No. PCT/GB2021/051288, filed on May 27, 2021.
Claims priority of application No. 2008097 (GB), filed on May 29, 2020.
Prior Publication US 2023/0224285 A1, Jul. 13, 2023
Int. Cl. H04L 9/40 (2022.01); H04L 9/08 (2006.01)
CPC H04L 63/0442 (2013.01) [H04L 9/0869 (2013.01); H04L 63/1466 (2013.01); H04L 2209/04 (2013.01)] 18 Claims
OG exemplary drawing
 
1. A method for strengthening an asymmetric post-quantum encryption scheme to side channel attacks, comprising:
(a) generating a secret key comprising one or more values, wherein said secret key is generated in accordance with said asymmetric encryption scheme;
(b) generating a multiplicative mask and an additive mask, wherein said multiplicative mask is different from said additive mask, and wherein said multiplicative mask and said additive mask each comprises one or more values;
(c) generating a first key by multiplying each value of said one or more values of said secret key with a value of said one or more values of said multiplicative mask, wherein each of said one or more values of said secret key is processed by a different value of said one or more values of said multiplicative mask; and
(d) generating a second key by adding each value of said one or more values of said first key to a value of said one or more values of said additive mask, wherein each of said one or more values of said first key is processed by a different value of said one or more values of said additive mask;
during an encryption operation of the asymmetric post-quantum encryption scheme:
(e) multiplying a public matrix by the second key to generate a masked matrix; and
(f) generating a ciphertext; and
during a decryption operation of the asymmetric post-quantum encryption scheme:
(g) recovering a product of the secret key and the public matrix by:
(i) multiplying the public matrix by the additive mask to generate a first resultant matrix;
(ii) subtracting the first resultant matrix from the masked matrix to generate a second resultant matrix; and
(iii) multiplying the second resultant matrix by an inverse of the multiplicative mask to recover the product of the secret key and the public matrix.