ISO 8583 · Data fields

Field 64MAC

pyiso8583 starter profilesIndependent explanation

What this field describes

This field is labelled MAC and provides a message authentication code container in the selected profiles.

Binary and ASCII profiles use different representations. The library’s field length does not select the authentication algorithm, covered bytes or key.

Compare the two profiles

Container settings from the pinned pyiso8583 source.
Settingdefaultdefault_ascii
Value encodingBinaryASCII
Length limitExactly 8 bytesExactly 16 bytes
PrefixNoneNone

Length limits describe encoded values. They exclude any length prefix. The profiles can be customized; these settings do not establish the required fields or accepted values for a live connection.

Read the field boundary

Field 6416 bytesASCII value

Read exactly 16 value bytes. The next field begins immediately afterwards under this profile; no length prefix belongs to this field.

Find it in the bitmap

Bitmap
Primary
Position
64
Byte
8
Bit in byte
8

Positions start at one. Bits are counted from the most significant bit of each bitmap byte. This calculation locates the field’s presence indicator, not its value.