AES DESUSECV variable-length symmetric key token

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View a table showing the format of the DESUSECV variable-length symmetric key-token.

Table 1. AES DESUSECV variable-length symmetric key-token, version X'05'
Offset (bytes) Length (bytes) Description
Header
000 01 Token identifier:
Value
Meaning
X'02'
External key-token (encrypted payload is wrapped with a transport key or there is no payload). A transport key can be a key-encrypting key or an RSA public-key.

All unused values are reserved and undefined.
001 01 Reserved, binary zero.
002 02 Length in bytes of the overall token structure:

46 + (2 * kuf) + (2 * kmf) + kl + iead + uad + ((pl + 7) / 8)

Key token Minimum and maximum token length

External 46 + (2 * 1) + (2 * 1) + 0 + 11 + 0 + ((576 + 7) / 8) = 133
004 01

Token version number (identifies the format of this key token):

Value
Meaning
X'05'
Version 5 format of the key token (variable-length symmetric key-token)
005 03

Reserved, binary zero.
End of header
Wrapping information section (all data related to wrapping the key)
008 01 Key material state:
Value
Meaning
X'02'
Key is wrapped with a transport key. The transport key is an AES key-encrypting key. The key token is external.

All unused values are reserved and undefined.
009 01 Key verification pattern (KVP) type:
Value
Meaning
X'02'
KEK (8 leftmost bytes of SHA-256 hash: X'01 ∥ clear KEK). The key token is external.

All unused values are reserved and undefined.
010 16 KVP:

The field contains the KVP of the key-encrypting key used to wrap the key. The 8-byte KEK KVP is left-aligned in the field and padded on the right low-order bytes with binary zeros. The key token is external.
026 01 Encrypted section key-wrapping method (how data in the encrypted section is protected):
Value
Meaning
X'02'
AESKW (ANS X9.102). The key token is external with a key wrapped by an AES key-encrypting key.

All unused values are reserved and undefined.
027 01 Hash algorithm used for wrapping key. The value indicates the algorithm used to calculate the message digest of the associated data. The message digest is included in the wrapped payload and is calculated starting at offset 30 for the length in bytes of all the associated data for the key token (length value at offset 32).
Value
Meaning
X'02'
SHA-256

All unused values are reserved and undefined. The key token is external.
028 01 Payload format version (identifies format of the payload):
Value
Meaning
X'01'
V1 payload (V1PYLD). The payload is fixed length based on the maximum possible key size of the algorithm for the key. The key is padded with random data to the size of the largest key for that algorithm. This helps to deter attacks on keys known to be weaker. The key length cannot be inferred by the size of the payload. The key token is external or internal.

All unused values are reserved and undefined.
029 01 Reserved, binary zero.
End of wrapping information section
AESKW components: (1) associated data section and (2) optional wrapped AESKW payload
Associated data section
030 01 Associated data section version:
Value
Meaning
X'01'
Version 1 format of associated data
031 01 Reserved, binary zero.
032 02 Length in bytes of all the associated data for thekey token: 31.
034 01 Length in bytes of the optional key label (kl): 0.
035 01 Length in bytes of the optional IBM extended associated data (iead): 11.
036 01 Length in bytes of the optional user-definable associated data (uad): 0.
037 01 Reserved, binary zero.
038 02 Length in bits of the wrapped payload (pl): 576.

For an AESKW formatted payload, pl is based on the key size of the algorithm type and the payload format version:

DES algorithm (value at offset 41 is X'01')

A DES key can have a length of 8, 16, or 24 bytes (64, 128, 192 bits). A DES key in an AESKW formatted payload is always wrapped with a V1 payload and has a fixed length payload of 576 bits.
040 01 Reserved, binary zero.
041 01 Algorithm type (algorithm for which the key can be used):
Value
Meaning
X'01'
DES

All unused values are reserved and undefined.
042 02 Key type (general class of the key):
Value
Meaning
X'0008'
DESUSECV

All unused values are reserved and undefined.
044 01 Key usage fields count (kuf): 1. Key-usage field information defines restrictions on the use of the key.

Each key-usage field is 2 bytes in length. The value in this field indicates how many 2-byte key usage fields follow.
045 01 Key-usage field 1, high-order byte (reserved).

All bits are reserved and must be zero.
046 01 Key-usage field 1, low-order byte (reserved).

All bits are reserved and must be zero.
047 01 Key management fields count (kmf): 1. Key-management field information describes how the data is to be managed or helps with management of the key material.

Each key-management field is 2 bytes in length. The value in this field indicates how many 2-byte key management fields follow.
048 01 Key-management field 1, high-order byte (reserved).

All bits are reserved and must be zero.
049 01 Key-management field 1, low-order byte (reserved).

All bits are reserved and must be zero.
050 iead IBM® extended associated data: 
Offset  Length 	
(bytes) (bytes) Item 	             Contents
0 	     1 	     Structure version  X'00'
                identifier 	
1 	     1 	     Flag byte 1 	      Copy of flag byte 1 taken from
                                   offset 6 of the internal fixed-length
                                   DES source key token exported by the
                                   CSNDSYX verb into this external
                                   enciphered key.
2 	     1 	     Flag byte 2 	      Copy of flag byte 2 taken from offset 7
                                   of the internal fixed-length DES source
                                   key token exported by the CSNDSYX verb
                                   into this external enciphered key.
3 	     0 	     Masked control 	   Copy of 8 bytes of control vector taken
                vector             from offset 32 of the internal
                                   fixed-length DES source key token
                                   exported by the CSNDSYX verb into this
                                   external enciphered key. The key form
                                   bits (CV bits 40 - 42) are copied into
                                   the wrapped payload before being masked
                                   here to zero to conceal the length of the
                                   DES key.
End of associated data section
Optional wrapped AESKW formatted payload
061 72 Contents of payload: An encrypted payload which the Segment 2 code creates by wrapping the unencrypted AESKW formatted payload. The payload is made up of the integrity check value, pad length, length of hash options and hash, hash options, hash of the associated data, key material, and padding. The key token is internal.

A DES DESUSECV payload contains key material that is formatted. The key material is formatted as follows:

Offset  Length 	
bytes)  (bytes) Item 	             Contents
0 	     1 	     Key length (kl)    Value  Meaning
                                   X'08'  Single-length key
                                   X'10'  Double-length key
                                   X'18'  Triple-length key (IBM Z only)
1 	     1 	     Flag byte 1 	      Reserved, binary zero.
2 	     1 	     Flag byte 2 	      Value  Meaning
                                   B'xxxx xxx1'
                                          The key has guaranteed unique halves
                                   B'xxxx xxx0'
                                          The key does not have guaranteed
                                          unique halves.
                                   All unused bits are reserved and must be zero.
3        8      Left part of key   Left part of single-length, double-length,
                                   or (System z only) triple-length DES key.
11       8      Middle part of     Middle part of double-length or (IBM Z)
                key, or random     triple-length DES key, otherwise random data.
                data
19       8      Right part of      Right part of triple-length key (IBM Z only),
                key.               otherwise random data.
End of optional wrapped AESKW formatted payload
End of AESKW components
Note: All numbers are in big endian format.