pub unsafe fn sm4ed(rs1: u32, rs2: u32, const BS: u8) -> u32
riscv_ext_intrinsics
#114544)zksed
only.Expand description
Accelerates the block encrypt/decrypt operation of the SM4 block cipher [5, 31].
Implements a T-tables in hardware style approach to accelerating the SM4 round function. A byte is extracted from rs2 based on bs, to which the SBox and linear layer transforms are applied, before the result is XORβd with rs1 and written back to rd. This instruction exists on RV32 and RV64 base architectures. On RV64, the 32-bit result is sign extended to XLEN bits. This instruction must always be implemented such that its execution latency does not depend on the data being operated on.
Source: RISC-V Cryptography Extensions Volume I: Scalar & Entropy Source Instructions
Version: v1.0.1
Section: 3.43
Β§Note
The BS
parameter is expected to be a constant value and only the bottom 2 bits of bs
are
used.
Β§Safety
This function is safe to use if the zksed
target feature is present.
Β§Details
Accelerates the round function F
in the SM4 block cipher algorithm
This instruction is included in extension Zksed
. Itβs defined as:
SM4ED(x, a, BS) = x β T(ai)
... where
ai = a.bytes[BS]
T(ai) = L(Ο(ai))
bi = Ο(ai) = SM4-S-Box(ai)
ci = L(bi) = bi β (bi βͺ 2) β (bi βͺ 10) β (bi βͺ 18) β (bi βͺ 24)
SM4ED = (ci βͺ (BS * 8)) β x
where β
represents 32-bit xor, and βͺ k
represents rotate left by k
bits.
As is defined above, T
is a combined transformation of non linear S-Box transform Ο
and linear layer transform L
.
In the SM4 algorithm, the round function F
is defined as:
F(x0, x1, x2, x3, rk) = x0 β T(x1 β x2 β x3 β rk)
... where
T(A) = L(Ο(A))
B = Ο(A) = (SM4-S-Box(a0), SM4-S-Box(a1), SM4-S-Box(a2), SM4-S-Box(a3))
C = L(B) = B β (B βͺ 2) β (B βͺ 10) β (B βͺ 18) β (B βͺ 24)
It can be implemented by sm4ed
instruction like: