IDTECH SecureHead User Manual page 28

SecureHead SPI Interface with FPC User Manual
track 1 length
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track 2 length

track 3 length
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track 1 data

track 2 data

track 3 data
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Description:
Track 1, Track 2 and Track 3 Unencrypted Length
This one-byte value is the length of the original Track data. It indicates the number of bytes in
the Track masked data field. It should be used to separate Track 1, Track 2 and Track 3data
after decrypting Track encrypted data field.
Track 3 Unencrypted Length
This one-byte value indicates the number of bytes in Track 3 data field.
Track 1 and Track 2 Masked
Track data masked with the MaskCharID (default is '*'). The first PrePANID (up to 6 for BIN,
default is 4) and last PostPANID (up to 4, default is 4) characters can be in the clear
(unencrypted).
Track 1, Track 2 and Track 3 Encrypted
This field is the encrypted Track data, using either TDES-CBC or AES-CBC with initial vector
of 0. If the original data is not a multiple of 8 bytes for TDES or a multiple of 16 bytes for AES,
the reader right pads the data with 0.
The key management scheme is DUKPT or Fixed key. For DUKPT, the key used for
encrypting data is called the Data Key. Data Key is generated by first taking the DUKPT
Derived Key exclusive or'ed with 0000000000FF0000 0000000000FF0000 to get the resulting
intermediate variant key. The left side of the intermediate variant key is then TDES encrypted
with the entire 16-byte variant as the key. After the same steps are preformed for the right side
of the key, combine the two key parts to create the Data Key.
Encrypted Data Length
Track 1 and Track 2 data are encrypted as a single block. In order to get the number of bytes
for encrypted data field, we need to get Track 1 and Track 2 unencrypted length first. The field
length is always a multiple of 8 bytes for TDES or multiple of 16 bytes for AES. This value
will be zero if there was no data on both tracks or if there was an error decoding both tracks.
Once the encrypted data is decrypted, all padding 0 need to be removed. The number of bytes
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(1 byte, 0 for no track1 data)
(1 byte, 0 for no track2 data)
(1 byte, 0 for no track3 data)
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