AES MAC variable-length symmetric key token

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View a table showing the format of an AES MAC variable-length symmetric key token.

Table 1. AES MAC variable-length symmetric key-token, version X'05'

AES MAC variable-length symmetric key-token, version X'05'
Offset (bytes) Length (bytes) Description

Header

000

01

Token identifier:

Value
Meaning
X'01'
Internal key-token (encrypted key is wrapped with the master key or there is no payload).
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 token length without DK enabled
Skeleton
46 + (2 * 2) + (2 * 3) + 0 + 0 + 0 + 0 = 56
Encrypted V1 payload
46 + (2 * 2) + (2 * 3) + 0 + 0 + 0 + ((640 + 7) / 8) = 136
Key token
Minimum token length with DK enabled
Skeleton
46 + (2 * 3) + (2 * 3) + 0 + 0 + 0 + 0 = 58
Encrypted V1 payload
46 + (2 * 3) + (2 * 3) + 0 + 0 + 0 + ((640 + 7) / 8) = 138
Key token
Maximum token length without DK enabled
External*
46 + (2 * 2) + (2 * 3) + 64 + 0 + 255 + ((8192 + 7) / 8) = 1399
Internal
46 + (2 * 2) + (2 * 3) + 64 + 0 + 255 + ((640 + 7) / 8) = 455
Key token
Maximum token length with DK enabled
External*
46 + (2 * 3) + (2 * 3) + 64 + 0 + 255 + ((8192 + 7) / 8) = 1401
Internal
46 + (2 * 3) + (2 * 3) + 64 + 0 + 255 + ((640 + 7) / 8) = 457

*This assumes a PKOAEP2 key-wrapping method using a 8192-bit RSA transport key.

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'00'
No key is present. This is called a skeleton key-token. The key token is external or internal.
X'02'
Key is wrapped with a transport key. When the encrypted section key-wrapping method is AESKW (value at offset 26 is X'02'), the transport key is an AES key-encrypting key. When it is PKOAEP2 (value at offset 26 is X'03'), the transport key is an RSA public-key. The key token is external.
X'03'
Key is wrapped with the AES master-key. The encrypted section key-wrapping method is AESKW. The key token is internal.

All unused values are reserved and undefined.

009

01

Key verification pattern (KVP) type:

Value
Meaning
X'00'
No KVP (no key present or key is wrapped with an RSA public-key). The key token is external or internal.
X'01'
AESMK (8 leftmost bytes of SHA-256 hash: X'01 ∥ clear AES MK). The key token is internal.
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 (value depends on value of key material state, that is, the value at offset 8):

Value at offset 8
Value of KVP
X'00'
The key-material state is no key present. The field should be filled with binary zeros. The key token is external or internal.
X'02'
The key material state is the key is wrapped with a transport key. The value of the KVP depends on the value of the encrypted section key-wrapping method:
  • When the key-wrapping method is AESKW (value at offset 26 is X'02'), 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.
  • When the key-wrapping method is PKOAEP2 (value at offset 26 is X'03'), the value should be filled with binary zeros. The encoded message, which contains the key, is wrapped with an RSA public-key.

The key token is external.

X'03'
The key-material state is the key is wrapped with the AES master-key. The field contains the MKVP of the AES master-key used to wrap the key. The 8-byte MKVP is left-aligned in the field and padded on the right low-order bytes with binary zeros. The key token is internal.

All unused values are reserved and undefined.

026

01

Encrypted section key-wrapping method (how data in the encrypted section is protected):

Value
Meaning
X'00'
No key-wrapping method (no key present). The key token is external or internal.
X'02'
AESKW (ANS X9.102). The key token is external with a key wrapped by an AES key-encrypting key, or the key token is internal with a key wrapped by the AES master-key.
X'03'
PKOAEP2. Message M, which contains the key, is encoded using the RSAES-OAEP scheme of the RSA PKCS #1 v2.1 standard. The encoded message (EM) is produced using the given hash algorithm by encoding message M using the Bellare and Rogaway Optimal Asymmetric Encryption Padding (OAEP) method for encoding messages. For PKAOEP2, M is defined as follows:

M = [32 bytes: hAD] ∥ [2 bytes: bit length of the clear key] ∥ [clear key]

where hAD is the message digest of the associated data, and is calculated using the SHA-256 algorithm on the data starting at offset 30 for the length in bytes of all the associated data for the key token (length value at offset 32).

EM is wrapped with an RSA public-key. The key token is external.

All unused values are reserved and undefined.

027

01

Hash algorithm used for wrapping key or encoding message. Meaning depends on whether the encrypted section key-wrapping method (value at offset 26) is no key-wrapping method, AESKW, or PKOAEP2:

No key-wrapping method (value at offset 26 is X'00')

Hash algorithm used for wrapping key when encrypted section key-wrapping method is no key-wrapping method:

Value
Meaning
X'00'
No hash (no key present)

All unused values are reserved and undefined. The key token is external or internal.

AESKW key-wrapping method (value at offset 26 is X'02')

Hash algorithm used for wrapping key when encrypted section key-wrapping method is AESKW. 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 or internal.

PKOAEP2 key-wrapping method (value at offset 26 is X'03')

Hash algorithm used for encoding message when encrypted section key-wrapping method is PKOAEP2. The value indicates the given hash algorithm used for encoding message M using the RSAES-OAEP scheme of the RSA PKCS #1 v2.1 standard.

Value
Meaning
X'01'
SHA-1
X'02'
SHA-256
X'04'
SHA-384
X'08'
SHA-512

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 format depends on the encrypted section key-wrapping method (value at offset 26):
Value at offset 26
Meaning
X'00'
There is no key-wrapping method. When no key is present, there is no payload. The key token is external or internal.
X'02'
The key-wrapping method is AESKW and 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.
X'03'
The key-wrapping method is PKOAEP2 and the payload length is equal to the modulus size in bits of the RSA transport key used to wrap the encoded message. The key token is external. When the external key is exported, the internal target key will have the same V1 payload format.

All unused values are reserved and undefined.

029

01

Reserved, binary zero.

End of wrapping information section

AESKW or PKOAEP2 components: (1) associated data section and (2) optional wrapped AESKW formatted payload or wrapped PKOAEP2 encoded payload (no payload if no key present)

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 the key token: 26 - 347.

034

01

Length in bytes of the optional key label (kl): 0 or 64.

035

01

Length in bytes of the optional IBM extended associated data (iead): 0.

036

01

Length in bytes of the optional user-definable associated data (uad): 0 - 255.

037

01

Reserved, binary zero.

038

02

Length in bits of the wrapped payload (pl): 0, 512 - 4096.

  • For no key-wrapping method (no key present), pl is 0.
  • For PKOAEP2 encoded payloads, pl is the length in bits of the modulus size of the RSA key used to wrap the payload. This can be 512 - 4096.
  • For an AESKW formatted payload, pl is based on the key size of the algorithm type and the payload format version:

    AES algorithm (value at offset 41 is X'02')

    An AES key can have a length of 16, 24, or 32 bytes (128, 192, or 256 bits). The following table shows the payload length for a given AES key size and payload format:

                            Bit length of            Bit length of
                        V0 payload (value at     V1 payload (value at
AES key size            offset 28 is X'00')      offset 28 is X'01')
16 bytes (128 bits)     Not applicable           640
24 bytes (192 bits)     Not applicable           640
32 bytes (256 bits)     Not applicable           640

040

01

Reserved, binary zero.

041

01

Algorithm type (algorithm for which the key can be used):

Value
Meaning
X'02'
AES

All unused values are reserved and undefined.

042

02

Key type (general class of the key):

Value
Meaning
X'0002'
MAC

All unused values are reserved and undefined.

044

01

Key usage fields count (kuf): 2 - 3. Key-usage field information defines restrictions on the use of the key.

Count is based on whether the key is DK enabled or not:

DK enabled
kuf
No
2
Yes
3

Each key-usage field is 2 bytes in length. The value in this field indicates how many 2-byte key usage fields follow. Key-usage field information defines restrictions on the use of the key.

045

01

Key-usage field 1, high-order byte (MAC operation).

Value
Meaning
B'11xx xxxx'
For kuf > 2, if DK enabled (value at offset 50 = X'01') then this value is undefined or not used. Otherwise, key can be used for generate; key can be used for verify (GENERATE).
B'10xx xxxx'
Key can be used for generate; key cannot be used for verify (GENONLY).
B'01xx xxxx'
Key cannot be used for generate; key can be used for verify (VERIFY).
B'00xx xxxx'
Undefined or not used.

All unused bits are reserved and must be zero.

046

01

Key-usage field 1, low-order byte (user-defined extension control).

047

01

Key-usage field 2, high-order byte (MAC mode).

Value
Meaning
X'01'
CMAC mode (CMAC). NIST SP 800-38B.

All unused values are reserved and undefined.

048

01

Key-usage field 2, low-order byte: Reserved, or Authentication data verification, as follows:

  • Releases before 5.5, or MAC operation (KUF1 HOB) is not VERIFY: Reserved, binary zero.
  • Rlease 5.5 or later, and MAC operation (KUF1 HOB) is VERIFY: Authentication data verification
Value
Meaning
B'1xxx xxxx'
For key usage VERIFY, the key can be used by CSNBPTR2 to verify authentication data using NIST SP 800-38B block cipher-based MAC algorithm, called CMAC, for ISO-4 to ISO-4 PAN change (PTR2AUTH). A key with this usage can only be used by Encrypted PIN Translate and MAC Verify2.
B'0xxx xxxx'
For key usage VERIFY, if the command Encrypted PIN Translate2 - Permit ISO-4 to ISO-4 PTR2AUTH (offset X'0395') is enabled in the active role, the key cannot be used by CSNBPTR2 to verify authentication data using the CMAC algorithm for ISO-4 to ISO-4 PAN change (NOP2AUTH).

049, for kuf > 2

01

Key-usage field 3, high-order byte. The meaning is determined by the field format identifier (value at offset 50). Currently the only field format identifier is DK enabled:

DK enabled (value at offset 50 is X'01')

Common control:

Value
Meaning
X'01'
PIN_OP (DKPINOP)
X'03'
PIN_AD1 (DKPINAD1)
X'04'
PIN_AD2 (DKPINAD2)

All unused values are reserved and undefined.

050, for kuf > 2

01

Key-usage field 3, low-order byte (field format identifier). Identifies the format of key-usage field 3, high-order byte (value at offset 49):

Value
Meaning
X'01'
DK enabled (set when DKPINOP, DKPINAD1, or DKPINAD2 keyword is used)

All unused values are reserved and undefined.

045 + (2 * kuf)

01

Key management fields count (kmf): 3. 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.

046 + (2 * kuf)

01

Key-management field 1, high-order byte (symmetric-key export control).

047 + (2 * kuf)

01

Key-management field 1, low-order byte (export control by algorithm).

048 + (2 * kuf)

01

Key-management field 2, high-order byte (key completeness).

049 + (2 * kuf)

01

Key-management field 2, low-order byte (security history).

050 + (2 * kuf)

01

Key-management field 3, high-order byte (pedigree original).

051 + (2 * kuf)

01

Key-management field 3, low-order byte (pedigree current).

052 + (2 * kuf)

kl

Optional key label.

052 + (2 * kuf) + kl

iead

Optional IBM extended associated data (unused).

052 + (2 * kuf) + kl + iead

uad

Optional user-defined associated data.

End of associated data section

Optional wrapped AESKW formatted payload or wrapped PKOAEP2 encoded payload (no payload if no key present)

052 + (2 * kuf) + kl + iead + uad

(pl + 7) / 8

Contents of payload (pl is in bits) depending on the encrypted section key-wrapping method (value at offset 26):
Value at offset 26 Encrypted section key-wrapping method Meaning
X'02'

AESKW

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.
X'03'

PKOAEP2

An encrypted PKOAEP2 encoded payload created using the RSAES-OAEP scheme of the PKCS #1 v2.1 standard. The message M is encoded for a given hash algorithm using the Bellare and Rogaway Optimal Asymmetric Encryption Padding (OAEP) method for encoding messages. For PKAOEP2, M is defined as follows:

M = [32 bytes: hAD] ∥ [2 bytes: bit length of the clear key] ∥ [clear key]

where hAD is the message digest of the associated data, and is calculated using the SHA-256 algorithm starting at offset 30 for the length in bytes of all the associated data for the key token (length value at offset 32). The encoded message is wrapped with an RSA public-key according to the standard. The key token is external.

End of optional wrapped AESKW formatted payload or wrapped PKAOEP2 encoded payload

End of AESKW or PKOAEP2 components
Note: All numbers are in big endian format.