aesdecwide256kl

AES Decrypt Wide 256-bit Key Locker

AESDECWIDE256KL m128

Decrypts 8 blocks using 256-bit Key Locker handle.

Details

Decrypts 8 AES blocks (128 bits each) in parallel using a 256-bit Key Locker encrypted key handle stored at the memory operand. The ciphertext blocks are implicit in XMM0–XMM7 (input) and plaintext results are written back to XMM0–XMM7 (output). The ZF flag is set to 0 on success or 1 if the key handle is invalid.

Pseudocode Operation

key_handle = load_from_memory_128bit(m128);
if (key_handle_invalid(key_handle)) {
  ZF = 1;
} else {
  for i = 0 to 7 {
    XMM[i] = AES_decrypt_block_256bit_key(XMM[i], key_handle);
  }
  ZF = 0;
}

Example

AESDECWIDE256KL [rbp-16]

Encoding

Binary Layout

Format Legacy

Opcode F3 0F 38 D8 !(11):011:bbb

Extension KEYLOCKER_WIDE

Operands

dest
128-bit memory operand

Reference (Intel® SDM)

Instruction Forms

Opcode	Instruction	Op/En	64/32-bit Mode	CPUID	Description
F3 0F 38 D8 !(11):011:bbb	AESDECWIDE256KL m512, <XMM0-7>	A	V/V	AES_WIDE	Decrypt XMM0-7 using 256-bit AES key indicated by handle at m512 and store each resultant block back to its corresponding register.

Instruction Operand Encoding

Op/En	Operand 1	Operand 2	Operand 3
A	N/A	ModRM:r/m (r)	Implicit XMM0-7 (r, w)

Description

The AESDECWIDE256KL1 instruction performs 14 rounds of AES to decrypt each of the eight blocks in XMM0-7 using the 256-bit key indicated by the handle from the second operand. It replaces each input block in XMM0-7 with its corresponding decrypted block if the operation succeeds (e.g., does not run into a handle violation failure).

Operation

AESDECWIDE256KL
Handle := UnalignedLoad of 512 bit (SRC);      // Load is not guaranteed to be atomic.
Illegal Handle = (HandleReservedBitSet (Handle) ||
(Handle[0] AND (CPL > 0)) ||
Handle [2] ||
HandleKeyType (Handle) != HANDLE_KEY_TYPE_AES256);
IF (Illegal Handle) {
THEN RFLAGS.ZF := 1;
ELSE
(UnwrappedKey, Authentic) := UnwrapKeyAndAuthenticate512 (Handle[511:0], IWKey);
IF (Authentic == 0)
THEN RFLAGS.ZF := 1;
ELSE
XMM0 := AES256Decrypt (XMM0, UnwrappedKey) ;
XMM1 := AES256Decrypt (XMM1, UnwrappedKey) ;
XMM2 := AES256Decrypt (XMM2, UnwrappedKey) ;
XMM3 := AES256Decrypt (XMM3, UnwrappedKey) ;
XMM4 := AES256Decrypt (XMM4, UnwrappedKey) ;
XMM5 := AES256Decrypt (XMM5, UnwrappedKey) ;
XMM6 := AES256Decrypt (XMM6, UnwrappedKey) ;
XMM7 := AES256Decrypt (XMM7, UnwrappedKey) ;
RFLAGS.ZF := 0;
FI;
FI;
RFLAGS.OF, SF, AF, PF, CF := 0;

Intel C/C++ Compiler Intrinsic Equivalent

AESDECWIDE256KLunsigned char _mm_aesdecwide256kl_u8(__m128i odata[8], const __m128i idata[8], const void* h);
Exceptions (All Operating Modes)
#UD                     If the LOCK prefix is used.
If CPUID.07H.00H:ECX.KEY_LOCKER[23] = 0.
If CR4.KL = 0.
If CPUID.19H:EBX.AESKLE[0] = 0.
If CR0.EM = 1.
If CR4.OSFXSR = 0.
If CPUID.19H:EBX.AES_WIDE[2] = 0.
#NM                    If CR0.TS = 1.
#PF                     If a page fault occurs.
#GP(0)                 If a memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit.
If the DS, ES, FS, or GS register is used to access memory and it contains a NULL segment
selector.
If the memory address is in a non-canonical form.
#SS(0)                 If a memory operand effective address is outside the SS segment limit.
If a memory address referencing the SS segment is in a non-canonical form.
AESDECWIDE256KL—Perform 14 Rounds of AES Decryption Flow With Key Locker on 8 Blocks Using 256-Bit Key                           Vol. 2A 3-44

Flags Affected

ZF is set to 0 if the operation succeeded and set to 1 if the operation failed due to a handle violation. The other arithmetic flags (OF, SF, AF, PF, CF) are cleared to 0. 1. Further details on Key Locker and usage of this instruction can be found here: https://software.intel.com/content/www/us/en/develop/download/intel-key-locker-specification.html. AESDECWIDE256KL—Perform 14 Rounds of AES Decryption Flow With Key Locker on 8 Blocks Using 256-Bit Key Vol. 2A 3-43