The EFS_KEY_INFO type is used to represent information about a key of a symmetric cryptosystem.

 typedef struct {
   DWORD dwVersion;
   unsigned long Entropy;
   ALG_ID Algorithm;
   unsigned long KeyLength;

dwVersion: The version of this data structure. It MUST be equal to 0x00000001.

Entropy: The actual number of bits of entropy or true randomness in the key. This value, divided by 8, MUST be less than or equal to the value of the KeyLength member.

Algorithm: The cryptographic algorithm with which the key is intended to be used.

KeyLength: The total length, in bytes, of the key. This value, multiplied by 8, MUST be greater than or equal to the value of the Entropy member. Valid combinations of Entropy, Algorithm, and KeyLength are specified in section 2.2.13.