31 lines
1.6 KiB
Rust
31 lines
1.6 KiB
Rust
//! Custom polynomial S-Box: S(x) = 192x^6 + 224x^5 + 120x^4 + 200x^3 + 150x^2 + 65x + 147 (mod 256)
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//! Corresponds to pow_main_dispatch State 0x0E/0x0F
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//! Evidence: constants 0xE0, 0x78, -0x40, 0x86838DC8, 0x96, 0x41, 0x93
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/// Apply polynomial S-Box to each byte of a 32-byte buffer.
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/// Decompiled:
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/// iVar4 = iVar1 * iVar1; // x^2
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/// iVar10 = iVar4 * iVar4; // x^4
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/// result = iVar1 * iVar10 * 0xe0 // 224*x^5
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/// + iVar10 * 0x78 // 120*x^4
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/// + iVar10 * iVar4 * -0x40 // -64*x^6 = 192*x^6 (mod 256)
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/// + ((iVar1 * 0x86838DC8 + 0x96) * iVar1 + 0x41) * iVar1
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/// + 0x93;
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pub fn apply_polynomial_sbox(buf: &mut [u8; 32]) {
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for b in buf.iter_mut() {
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let x = *b as u32;
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let x2 = x.wrapping_mul(x);
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let x4 = x2.wrapping_mul(x2);
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let result = x.wrapping_mul(x4).wrapping_mul(0xE0) // 224*x^5
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.wrapping_add(x4.wrapping_mul(0x78)) // 120*x^4
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.wrapping_add(x4.wrapping_mul(x2).wrapping_mul(0xFFFF_FFC0)) // 192*x^6 (-64 mod 2^32)
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.wrapping_add(
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x.wrapping_mul(0x86838DC8_u32).wrapping_add(0x96) // 200*x + 150
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.wrapping_mul(x).wrapping_add(0x41) // *x + 65
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.wrapping_mul(x) // -> 200x^3+150x^2+65x
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)
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.wrapping_add(0x93); // + 147
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*b = result as u8;
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}
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}
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