Censys — Internet Asset Discovery

Censys continuously scans the public internet and indexes detailed metadata about every reachable host: open ports, running services, TLS certificates, and BGP routing information. Complementary to Shodan with different scanner vantage points and richer certificate data.

Requires: CENSYS_API_ID and CENSYS_API_SECRET — free tier at https://search.censys.io/register (0.4 req/sec, 250 queries/month).

When to Use

• Look up what Censys sees on a specific IP address
• Discover internet-exposed assets for a given organisation or ASN
• Investigate TLS certificates — find all hosts sharing a certificate or subject
• Security audit: verify which services are visible from the public internet
• User asks "what does Censys show for IP X", "find hosts with this certificate", "look up ASN exposure"

How to Use

Look up a specific host by IP

powershell
$ip       = "8.8.8.8"
$id       = $env:CENSYS_API_ID
$secret   = $env:CENSYS_API_SECRET
$b64      = [Convert]::ToBase64String([Text.Encoding]::UTF8.GetBytes("${id}:${secret}"))
$headers  = @{ Authorization = "Basic $b64" }

$result = Invoke-RestMethod -Uri "https://search.censys.io/api/v2/hosts/$ip" -Headers $headers
$r      = $result.result
Write-Host "IP:           $($r.ip)"
Write-Host "AS:           $($r.autonomous_system.name) (ASN $($r.autonomous_system.asn))"
Write-Host "Country:      $($r.location.country)"
Write-Host "Open ports:"
$r.services | ForEach-Object {
    Write-Host "  $($_.port)/$($_.transport_protocol) — $($_.service_name)"
}

Search with a query string

powershell
$query    = "services.service_name: HTTP and location.country_code: IN"
$b64      = [Convert]::ToBase64String([Text.Encoding]::UTF8.GetBytes("$($env:CENSYS_API_ID):$($env:CENSYS_API_SECRET)"))
$headers  = @{ Authorization = "Basic $b64" }
$encoded  = [Uri]::EscapeDataString($query)

$result = Invoke-RestMethod -Uri "https://search.censys.io/api/v2/hosts/search?q=$encoded" -Headers $headers
Write-Host "Total matches: $($result.result.total)"
$result.result.hits | Select-Object -First 10 | ForEach-Object {
    Write-Host "  $($_.ip) — $($_.autonomous_system.name) ($($_.location.country_name))"
}

Look up a TLS certificate by SHA-256 fingerprint

powershell
$sha256  = "YOUR_CERT_SHA256_HERE"
$b64     = [Convert]::ToBase64String([Text.Encoding]::UTF8.GetBytes("$($env:CENSYS_API_ID):$($env:CENSYS_API_SECRET)"))
$headers = @{ Authorization = "Basic $b64" }

$result = Invoke-RestMethod -Uri "https://search.censys.io/api/v2/certificates/$sha256" -Headers $headers
$parsed = $result.result.parsed
Write-Host "Subject:   $($parsed.subject_dn)"
Write-Host "Issuer:    $($parsed.issuer_dn)"
Write-Host "Valid:     $($parsed.validity.start) → $($parsed.validity.end)"
Write-Host "SANs:      $($parsed.names_from_san -join ', ')"

Examples

"What is exposed on IP 1.2.3.4?" → Host lookup: returns open ports, service names, ASN, and location.

"Find all exposed Redis servers in Germany" → Query: services.service_name: REDIS and location.country_code: DE

"Who else uses this TLS certificate?" → Certificate lookup by SHA-256 fingerprint — shows SAN names and validity.

"Show me all hosts in ASN 15169" → Query: autonomous_system.asn: 15169

Cautions

• Free tier: 250 queries/month, 0.4 req/sec — pace bulk operations with Start-Sleep -Milliseconds 2500
• Censys data reflects last scan date — real-time state may differ
• Host lookup counts against your monthly quota
• Certificate search may return expired or revoked certs — check validity dates
• Never use Censys results to attempt unauthorised access; recon and awareness only

Requirements

• CENSYS_API_ID and CENSYS_API_SECRET — free account at https://search.censys.io/register