Certificate decoder

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Certificate decoder

What a certificate says about itself. The signature is not checked, and it says so.

It runs entirely in this browser tab: the passwords, keys and messages you type are never uploaded, and the tool makes no network request while it works. Open your browser's network panel and try it — nothing leaves the page.

What it takes

A PEM document.

An example

-----BEGIN CERTIFICATE-----
MIIAijB3oAMCAQICAwECAzALBgkqhkiG9w0BAQswFzEVMBMGA1UEAwwMRXhhbXBs
ZSBSb290MB4XDTI1MDEwMTAwMDAwMFoXDTI2MDEwMTAwMDAwMFowFjEUMBIGA1UE
AwwLZXhhbXBsZS5jb20wDTALBgkqhkiG9w0BAQEwCwYJKoZIhvcNAQELAwIAAQ==
-----END CERTIFICATE-----

Settings

Show the other names
The names a browser actually checks. It has not looked at the common name since 2017.

How to use it

  1. Paste your text into the box above, or open a file.
  2. Adjust the settings beside it until the result is what you wanted.
  3. Copy the result, or save it as a file. The result updates as you type.

Questions

Is this audited cryptography?
No, and every result that rests on a cipher says so. Each algorithm here matches the vectors its own standard publishes, which proves it computes the right function; it does not prove there is no timing leak, and no test in this workspace could. For anything that matters, use an implementation somebody has reviewed.
Is what I type uploaded anywhere?
No. The whole tool is carried as WebAssembly and runs on your own device. No password, key, message or certificate is sent anywhere, and nothing is stored beyond the settings you chose.
Why does a tool ask me for a word list?
Because shipping one would be worse than not. A usable list of common passwords is bigger than everything else on this page put together, and a small one is actively harmful — it calls a leaked password uncommon. Paste your own and it is used, and it does not leave the page either.
Does a check here mean my key is safe?
It means the shape matched or the arithmetic came out. A scanner finds what it was written to find; a certificate that parses is well formed, not trusted; a password that is not in your list is a password nobody has leaked yet. Each tool says which of those it just told you.

Other tools for looking at what is there

Secret scanner
Keys and tokens with a published shape, found in a pasted file.

Base32 and Base58
The same bytes in five alphabets, and what each one was invented for.

All eighteen tools