AES CIPHER variable-length symmetric key token

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View a table showing the format of the CIPHER variable-length symmetric key-token that can be used with the AES algorithm. An AES CIPHER key-token is used by the Symmetric Algorithm Decipher (CSNBSAD) and Symmetric Algorithm Encipher (CSNBSAE) verbs to decipher or encipher data with the AES algorithm.

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

AES CIPHER variable-length symmetric key-token, version X'05'
Offset (bytes) Length (bytes) Description
000 01 Token identifier:
Value
Meaning
X'01'
Internal key-token (encrypted key is wrapped with the master key, the key is clear, or there is no payload).
X'02'
External key-token (encrypted payload is wrapped with a transport key, the payload is clear, 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
Skeleton
46 + (2 * 2) + (2 * 3) + 0 + 0 + 0 + 0 = 56
Clear V0 payload
46 + (2 * 2) + (2 * 3) + 0 + 0 + 0 + ((128 + 7) / 8) = 72
Encrypted V0 payload
46 + (2 * 2) + (2 * 3) + 0 + 0 + 0 + ((512 + 7) / 8) = 120
Encrypted V1 payload
46 + (2 * 2) + (2 * 3) + 0 + 0 + 0 + ((640 + 7) / 8) = 136
Key token
Maximum token length
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

*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'01'
Key is clear. 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, key is clear, 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'01'
The key-material state is key is clear. 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.
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 or key is clear). 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 or key is clear).

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). Release 4.4 or later, otherwise undefined.
Value
Meaning
X'00'
V0 payload (V0PYLD). 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. When the key is clear, the payload is unformatted. The key token is external or internal.
X'02'
The key-wrapping method is AESKW and the payload is variable length. The payload is formatted with the minimum size possible to contain the key material. The payload length varies for a given algorithm and key type. The key length can 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 V0 payload format.
X'01'
V1 payload (Release 4.4 or later). 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. When the key is clear, the payload is unformatted. 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
Clear key, AESKW, or PKOAEP2 components: (1) associated data section and (2) optional clear key payload, 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 - 345.
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 clear or wrapped payload (pl): 0, 128, 192, 256, 512 - 4096.
  • For no key-wrapping method (no key present or key is clear), pl is the length in bits of the key. For no key present, pl is 0. For key is clear, pl can be 128, 192, or 256.
  • 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 V0 payload       Bit length of V1 payload
AES key size            (value at offset 28 is X'00'   (value at offset 28 is X'01')
16 bytes (128 bits)     512                            640
24 bytes (192 bits)     576                            640
32 bytes (256 bits)     640                            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'0001'
CIPHER

All unused values are reserved and undefined.
044 01 Key usage fields count (kuf): 2. 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 (encryption and translation control):
Value
Meaning
B'1xxx xxxx'
Key can be used for encryption (ENCRYPT).
B'0xxx xxxx'
Key cannot be used for encryption.
B'x1xx xxxx'
Key can be used for decryption (DECRYPT).
B'x0xx xxxx'
Key cannot be used for decryption.
B'xx1x xxxx'
Key can be used for data translate (C-XLATE).
B'xx0x xxxx'
Key cannot be used for data translate.
B'00xx xxxx'
Undefined or not used.
B'000x 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). Refer to Table 1.
047 01 Key-usage field 2, high-order byte (encryption mode):
Value
Meaning
X'00'
Key can be used for Cipher Block Chaining (CBC).
X'01'
Key can be used for Electronic Code Book (ECB).
X'02'
Key can be used for Cipher Feedback (CFB).
X'03'
Key can be used for Output Feedback (OFB).
X'04'
Key can be used for Galois/Counter Mode (GCM).
X'05'
Key can be used for Xor-Encrypt-Xor-based Tweaked Stealing (XTS).
X'06'
Key can be used for Format Preserving method FF1.
X'07'
Key can be used for Format Preserving method FF2.
X'08'
Key can be used for Format Preserving method FF2.1.
X'FF'
Key can be used for any encryption mode (ANY-MODE).

All unused values are reserved and undefined.
048 01 Key-usage field 2, low-order byte (reserved). All bits are reserved and must be zero.
049 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.
050 01 Key-management field 1, high-order byte (symmetric-key export control). Refer to Table 1.
051 01 Key-management field 1, low-order byte (export control by algorithm). Refer to Table 1.
052 01 Key-management field 2, high-order byte (key completeness). Refer to Table 1.
053 01 Key-management field 2, low-order byte (security history). Refer to Table 1.
054 01 Key-management field 3, high-order byte (pedigree original). Refer to Table 1.
055 01 Key-management field 3, low-order byte (pedigree current). Refer to Table 1.
056 kl Optional key label.
056 + kl iead Optional IBM extended associated data.
056 + kl + iead uad Optional user-defined associated data.
End of associated data section
Optional clear key payload, wrapped AESKW formatted payload, or wrapped PKOAEP2 encoded payload (no payload if no key present)
056 + 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'00' No key-wrapping method. Only applies when key is clear (key material state (value at offset 8) is X'01'). Only the key material is in the payload. The key token is external or internal.
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 clear key payload, wrapped AESKW formatted payload, or wrapped PKOAEP2 encoded payload
End of clear key, AESKW, or PKOAEP2 components
Note: All numbers are in big endian format.