41-84 Vol. 3D

SGX INSTRUCTION REFERENCES

EGETKEY—Retrieves a Cryptographic Key 

Instruction Operand Encoding

Description

The ENCLU[EGETKEY] instruction returns a 128-bit secret key from the processor specific key hierarchy. The 
register RBX contains the effective address of a KEYREQUEST structure, which the instruction interprets to deter-
mine the key being requested. The Requesting Keys section below provides a description of the keys that can be 
requested. The RCX register contains the effective address where the key will be returned. Both the addresses in 
RBX & RCX should be locations inside the enclave. 
EGETKEY derives keys using a processor unique value to create a specific key based on a number of possible inputs. 
This instruction leaf can only be executed inside an enclave.

EEGETKEY Memory Parameter Semantics

After validating the operands, the instruction determines which key is to be produced and performs the following 
actions:

•

The instruction assembles the derivation data for the key based on the Table 41-56

•

Computes derived key using the derivation data and package specific value

•

Outputs the calculated key to the address in RCX

The instruction fails with #GP(0) if the operands are not properly aligned. Successful completion of the instruction 
will clear RFLAGS.{ZF, CF, AF, OF, SF, PF}. The instruction returns an error code if the user tries to request a key 
based on an invalid CPUSVN or ISVSVN (when the user request is accepted, see the table below), requests a key 
for which it has not been granted the attribute to request, or requests a key that is not supported by the hardware. 
These checks may be performed in any order. Thus, an indication by error number of one cause (for example, 
invalid attribute) does not imply that there are not also other errors. Different processors may thus give different 
error numbers for the same Enclave. The correctness of software should not rely on the order resulting from the 
checks documented in this section. In such cases the ZF flag is set and the corresponding error bit 
(SGX_INVALID_SVN, SGX_INVALID_ATTRIBUTE, SGX_INVALID_KEYNAME) is set in RAX and the data at the 
address specified by RCX is unmodified.
Requesting Keys
The KEYREQUEST structure (see Section 38.17.1) identifies the key to be provided. The Keyrequest.KeyName field 
identifies which type of key is requested. 
Deriving Keys
Key derivation is based on a combination of the enclave specific values (see Table 41-56) and a processor key. 
Depending on the key being requested a field may either be included by definition or the value may be included 
from the KeyRequest. A “yes” in Table 41-56 indicates the value for the field is included from its default location, 
identified in the source row, and a “request” indicates the values for the field is included from its corresponding 
KeyRequest field. 

Opcode/

Instruction

Op/En

64/32 

bit Mode 

Support

CPUID 

Feature 

Flag

Description

 EAX = 04H

IR

V/V

SGX1

This leaf function retrieves a cryptographic key.

ENCLU[EGETKEY]

Op/En

EAX

RBX

RCX

IR

EGETKEY (In)

Address to a KEYREQUEST (In)

Address of the OUTPUTDATA (In)

KEYREQUEST

OUTPUTDATA

 Enclave read access

 Enclave write access