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tessl/npm-lapo--asn1js

Generic ASN.1 parser/decoder that can decode any valid ASN.1 DER or BER structures.

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Overview
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cli-usage.mddocs/

CLI Usage

Command-line tool for dumping and analyzing ASN.1 structures from files or data URIs with colored output and RFC definition matching.

Capabilities

Command Line Interface

The dumpASN1 command provides a powerful CLI tool for analyzing ASN.1 structures with colored terminal output and automatic definition matching.

# Install and use via npx (recommended)
npx @lapo/asn1js <filename|data-uri>

# If installed globally
dumpASN1 <filename|data-uri>

# Local execution (if you have the source)
./dumpASN1.js <filename|data-uri>

Usage Examples:

# Analyze a certificate file
npx @lapo/asn1js certificate.crt

# Analyze a private key
npx @lapo/asn1js private-key.der

# Analyze from data URI
npx @lapo/asn1js "data:base64,MIICIjANBgkqhkiG9w0BAQEFAAOCAg8AMIICCgKCAgEA..."

# Analyze PEM file
npx @lapo/asn1js server.pem

# Analyze any binary ASN.1 file
npx @lapo/asn1js structure.asn1

Input Format Support

The CLI tool automatically detects and handles multiple input formats:

  • Binary files: Raw ASN.1 DER/BER encoded files
  • PEM files: Files with -----BEGIN ... -----END armoring
  • Data URIs: data:base64,<base64-data> format for inline data
  • Base64 files: Files containing raw base64 encoded ASN.1 data
# Examples of different file types it can handle
npx @lapo/asn1js certificate.crt     # X.509 certificate
npx @lapo/asn1js private.key         # Private key file
npx @lapo/asn1js public.pem          # PEM-encoded public key
npx @lapo/asn1js csr.der             # Certificate signing request
npx @lapo/asn1js ca-bundle.pem       # Certificate bundle
npx @lapo/asn1js timestamp.tsr       # Timestamp response
npx @lapo/asn1js signed.p7s          # PKCS#7 signed data

Output Features

The CLI tool provides rich formatted output with the following features:

Colored Terminal Output

  • Type names: Highlighted in yellow for easy identification
  • Element names: Definition names in blue when matched against RFC definitions
  • Position markers: Shows byte positions for debugging
  • Content preview: Formatted content display with proper encoding

Structure Analysis

  • Hierarchical display: Indented tree structure showing ASN.1 nesting
  • Position information: Byte offsets for each element (@position+length)
  • Construction indicators: Shows whether elements are constructed or primitive
  • Encapsulation detection: Identifies when OCTET_STRING or BIT_STRING contain nested ASN.1

RFC Definition Matching

  • Automatic matching: Attempts to match structures against known RFC definitions
  • Common structure recognition: Identifies certificates, keys, signatures, etc.
  • Definition names: Shows standardized names for recognized structures
  • Confidence scoring: Indicates how well the structure matches known patterns

Example Output

$ npx @lapo/asn1js certificate.crt

SEQUENCE @0+1234 (constructed)
  SEQUENCE @4+954 (constructed): tbsCertificate
    [0] @8+3 (constructed): version
      INTEGER @10+1: 2
    INTEGER @13+20: serialNumber
      01:23:45:67:89:AB:CD:EF:01:23:45:67:89:AB:CD:EF:01:23:45:67
    SEQUENCE @35+13 (constructed): signature
      OBJECT_IDENTIFIER @37+9: 1.2.840.113549.1.1.11 | sha256WithRSAEncryption
      NULL @48+0
    SEQUENCE @50+156 (constructed): issuer
      SET @52+31 (constructed)
        SEQUENCE @54+29 (constructed)
          OBJECT_IDENTIFIER @56+3: 2.5.4.6 | countryName
          PrintableString @61+2: US
      SET @85+45 (constructed)
        SEQUENCE @87+43 (constructed)
          OBJECT_IDENTIFIER @89+3: 2.5.4.10 | organizationName
          UTF8String @94+36: Example Organization
    ...
  SEQUENCE @960+13 (constructed): signatureAlgorithm  
    OBJECT_IDENTIFIER @962+9: 1.2.840.113549.1.1.11 | sha256WithRSAEncryption
    NULL @973+0
  BIT_STRING @975+257 (encapsulates): signatureValue
    00:A1:B2:C3:D4:E5:F6:07:18:29:3A:4B:5C:6D:7E:8F:90:...

Advanced Usage Patterns

Processing Multiple Files

# Process multiple certificates
find /etc/ssl/certs -name "*.pem" -exec npx @lapo/asn1js {} \;

# Compare two certificates
npx @lapo/asn1js cert1.pem > cert1.dump
npx @lapo/asn1js cert2.pem > cert2.dump
diff cert1.dump cert2.dump

Integration with Other Tools

# Extract certificate from TLS connection and analyze
echo | openssl s_client -connect example.com:443 2>/dev/null | \
  openssl x509 -outform DER | \
  base64 | \
  xargs -I {} npx @lapo/asn1js "data:base64,{}"

# Analyze certificate chain
openssl s_client -connect example.com:443 -showcerts 2>/dev/null | \
  awk '/BEGIN CERT/,/END CERT/' | \
  npx @lapo/asn1js

# Create and analyze a CSR
openssl req -new -key private.key -out request.csr -subj "/CN=example.com"
npx @lapo/asn1js request.csr

Error Handling and Debugging

The CLI tool provides detailed error messages for common issues:

# File not found
$ npx @lapo/asn1js nonexistent.crt
Error: Cannot read file 'nonexistent.crt'

# Invalid ASN.1 structure
$ npx @lapo/asn1js invalid.txt
Error: Invalid ASN.1 structure at position 0

# Corrupted data
$ npx @lapo/asn1js corrupted.der
Error: Container at offset 45 has a length of 1000, which is past the end of the stream

Output Redirection and Processing

# Save analysis to file
npx @lapo/asn1js certificate.crt > analysis.txt

# Extract specific information using grep
npx @lapo/asn1js certificate.crt | grep "OBJECT_IDENTIFIER"

# Count different ASN.1 types
npx @lapo/asn1js certificate.crt | grep -o '\w\+String\|INTEGER\|SEQUENCE\|SET' | sort | uniq -c

# Find all OIDs in a structure
npx @lapo/asn1js certificate.crt | grep "OBJECT_IDENTIFIER" | cut -d: -f2 | cut -d'|' -f1

Performance Considerations

The CLI tool is optimized for:

  • Large files: Efficiently handles large ASN.1 structures (multi-MB certificate bundles)
  • Memory usage: Uses streaming approach to minimize memory footprint
  • Speed: Fast parsing and analysis even for complex nested structures
# Analyze large certificate bundle
npx @lapo/asn1js ca-bundle.pem  # Works efficiently even with 100+ certificates

# Process very large ASN.1 file
npx @lapo/asn1js large-structure.der  # Handles files up to several MB

Integration Examples

Shell Scripts

#!/bin/bash
# Certificate validation script
CERT_FILE="$1"

if [ ! -f "$CERT_FILE" ]; then
  echo "Certificate file not found: $CERT_FILE"
  exit 1
fi

echo "Analyzing certificate: $CERT_FILE"
npx @lapo/asn1js "$CERT_FILE"

# Extract subject name
SUBJECT=$(npx @lapo/asn1js "$CERT_FILE" | grep -A5 "subject" | grep "UTF8String\|PrintableString" | head -1)
echo "Subject: $SUBJECT"

Python Integration

import subprocess
import sys

def analyze_asn1(file_path):
    """Analyze ASN.1 file using @lapo/asn1js CLI tool"""
    try:
        result = subprocess.run(
            ['npx', '@lapo/asn1js', file_path],
            capture_output=True,
            text=True,
            check=True
        )
        return result.stdout
    except subprocess.CalledProcessError as e:
        return f"Error: {e.stderr}"

# Usage
analysis = analyze_asn1('certificate.crt')
print(analysis)

docs

cli-usage.md

core-parsing.md

dom-visualization.md

format-support.md

index.md

stream-processing.md

tile.json