z/OS Cryptographic Services ICSF System Programmer's Guide
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ECC Key Token Format

z/OS Cryptographic Services ICSF System Programmer's Guide
SA22-7520-17

The following table presents the format of the ECC Key Token.

Table 70. ECC Key Token Format
Offset (Dec)Number of BytesDescription
Token Header
000001Token identifier.
X'00'
Null token
X'1E'
External token
X'1F'
Internal token; the private key is protected by the master key
001001Version, X'00'.
002002Length of the key token structure excluding the internal information section.
004004Ignored; should be zero.
ECC Token Private section
000001X'20', section identifier, ECC private key
001001X'00', version.
002002Section length.
004001Wrapping Method: This value indicates the wrapping method used to protect the data in the encrypted section. It is not the method used to protect the Object Protection Key (OPK).
X'00'
Clear - section is unencrypted.
X'01'
AESKW
X'02'
CBC Wrap - Other
005001Hash used for Wrapping
X'01'
SHA224
X'02'
SHA256
X'04'
Reserved.
X'08 '
Reserved
006002Reserved Binary Zero
008001Key Usage:
X'C0'
Key Agreement
X'80'
Both signature generation and key agreement
X'00'
Signature generation only
X'02'
Translate allowed
The two high-order bits indicate permitted key usage in the decryption of symmetric keys and in the generation of digital signatures. The bit in the second nibble indicates if the key is translatable. A key is translatable if it can be re-encrypted from one key encrypting key to another.
009001Curve type:
X'00'
Prime curve
X'01'
Brainpool curve
010001Key Format and Security Flag.

External Token:

X'40'
Unencrypted ECC private key identifier
X'42'
Encrypted ECC private key identifier

Internal Token:

X'08'
Encrypted ECC private key identifier
011001Reserved Binary Zero
012002Length of p in bits
X'00C0'
Prime P-192
X'00E0'
Prime P-224
X'0100'
Prime P-256
X'0180'
Prime P-384
X'0209'
Prime P-521
X'00A0'
Brainpool p-160
X'00C0'
Brainpool P-192
X'00E0'
Brainpool P-224
X'0100'
Brainpool P-256
X'0140'
Brainpool P-320
X'0180'
Brainpool P-384
X'0200'
Brainpool P-512)
014002IBM Associated Data length. The length of this field must be greater than or equal to 16
016008External Token:
  • Unencrypted – Reserved Binary 0x'00'
  • Encrypted – KVP of the AESKEK

Internal Token: MKVP

024048External Token: reserved binary zeros.

Internal Token: Object Protection Key (OPK), ICV (Integrity Check value), 8 byte confounder and a 256-bit AES key used with the AESKW algorithm to encrypt the ECC private key.

The OPK is encrypted by the AES master key using AESKW as well. Example format for OPK data passed to AESKW:

  • 8 bytes = A6A6A6A6A6A60000
  • 40 bytes = Confounder(8)/Key(32)
072002Associated data length, aa
074002Length of formatted section in bytes, bb
076aaAssociated data (See Table 71 for the Associated Data format).
076 + aaStart of formatted sectionIf this section is in the clear it contains private key d.

If it is encrypted it contains the AESKW wrapped payload.

76 + aabbFormatted section which includes Private key d

See Table 72 for the format of the AESKW Wrapped Payload

76 + aa + bbEnd of formatted section
ECC Token Public Section
000001X'21', section identifier
001001X'00', version.
002002Section length
004004Reserved field, binary zero
008001Curve type
X'00'
Prime curve
X'01'
Brainpool curve
009001Reserved field, binary zero
010002Length of p in bits:
X'00C0'
Prime P-192
X'00E0'
Prime P-224
X'0100'
Prime P-256
X'0180'
Prime P-384
X'0209'
Prime P-521
X'00A0'
Brainpool P-160
X'00C0'
Brainpool P-192
X'00E0'
Brainpool P-224
X'0100'
Brainpool P-256
X'0140'
Brainpool P-320
X'0180'
Brainpool P-384
X'0200'
Brainpool P-512
012002This field is the length of the public key q value in bytes, the maximum value could be up to 133 bytes, cc. The value includes the key material length and one byte to indicate if the key material is compressed or uncompressed.
014ccPublic Key , q field

Associated Data Format for ECC Token

The table below defines the associated data as it is stored in the ECC token in the clear. Associated data is data whose integrity but not confidentiality is protected by a key wrap mechanism.

Table 71. Associated Data Format for ECC Private Key Token
Offset (Dec)Number of BytesDescription
000001Associated Data Version. 0 for ECC
001001Length of Key Label, kl
002002IBM Associated Data length, 16 + kl + xxx
004002IBM Extended Associated Data length, xxx
006001User Definable Associated Data length, yyy. User definable lengths are from 0 bytes to 100 bytes.
007001Curve Type
008002Length of p in bits
010001Usage flag
011001Format and Security flag
012004reserved
016klKey Label (optional)
016 + klxxxIBM Extended Associated Data
016 + kl + xxxyyyUser-definable Associated Data

AESKW Wrapped Payload Format for ECC Private Key Token

This table defines the contents of the AESKW payload: data will be copied into this format, then encrypted with the OPK according to the AESKW specification, and the result will be stored in the encrypted data section.

Table 72. AESKW Wrapped Payload Format for ECC Private Key Token
Offset (Dec)Number of BytesDescription
000006ICV (‘A6'....)
006001Length of padding in bits
007001Length of the hash of the associated data in bytes, ii
008004Hash options
012iiHash of Associated Data
12+iimmKey data
12+ii+mm0-7Padding to a multiple of 8 bytes

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