Description
Split a BER identifier's first octet.
ASN.1 encodings separate identifiers, lengths and contents, with DER applying stricter canonical forms than BER. One leading octet or terminal-bit check covers only part of the complete value.
Split a BER identifier's first octet.
When to use this tool
Use BER Tag First Octet Fields when inspecting a stated ASN.1 field or canonical-content condition.
How to use the tool and how it works
- Enter octet. Use the units and conventions below.
- Run the tool. Correct any format, range, or cross-field input error before interpreting the output.
- Read tagClass, constructed, tagNumber, highTagNumber. Inspect constructed, highTagNumber before interpreting the associated values.
Split a BER identifier's first octet. Require an octet; return top-two-bit tagClass, constructed flag and low-five-bit tagNumber, with highTagNumber true for 31.1
| Input field | Meaning and units | Accepted input |
|---|---|---|
| octet | One numeric octet, from 0 through 255. | Required. Safe integer; minimum 0; maximum 255. |
| Output field | Interpretation | Returned shape |
|---|---|---|
| tagClass | Tag Class | Required. Safe integer. |
| constructed | Constructed | Required. Boolean. |
| tagNumber | Tag Number | Required. Safe integer. |
| highTagNumber | High Tag Number | Required. Boolean. |
json
{
"input": {
"octet": 48
},
"output": {
"tagClass": 0,
"constructed": true,
"tagNumber": 16,
"highTagNumber": false
}
}Limitations and assumptions
- High-tag-number continuation octets and complete identifier canonicality are not checked.
- Inputs must satisfy both the field types and the cross-field conditions above. Invalid input causes an error; a successful false flag or documented placeholder is a different result.
- Numeric calculations use binary floating point unless exact decimal-integer arithmetic is explicitly stated. No hidden measurement tolerance or decimal rounding is added; nonfinite or out-of-contract results are rejected. Numeric signed-zero results are exported as zero.
Alternative or Complementary methods
Use an ASN.1 schema and complete BER/DER parser for nested values, canonicality and application meaning.
References
Similar or alternative tools
- Decoding: Ber Length Initial Octet
Inspect any BER initial length octet, including reserved FF.
- BER Length Short Long Discriminator
Classify an initial BER length octet.