ASN.1 Decoder

Parse DER/BER encoded data — X.509 certificates, CSRs, private keys — into a readable tree with OID names and a hex dump. 100% client-side.

DER / BER X.509 Certificates PEM & Base64 OID Resolver No Upload

Paste any PEM, Base64, or hex-encoded ASN.1 object and click Decode. The tree view shows every tag, length, and value with human-readable OID names. Switch to the Hex Dump tab to inspect the raw bytes.

Input — PEM / Base64 / Hex
Try an example
ASN.1 Structure

No structure yet

Paste ASN.1 data and click Decode.

Hex Dump

No hex dump yet

Decode some data first.

Frequently Asked Questions

ASN.1 (Abstract Syntax Notation One) is a standard interface description language for defining data structures serialized cross-platform. It is the foundation for X.509 certificates, CSRs, private keys, and virtually every cryptographic object in PKI. Data is encoded using DER or BER binary encoding rules.
DER (Distinguished Encoding Rules) is a strict subset of BER (Basic Encoding Rules) that guarantees a unique binary encoding for every ASN.1 value. DER is required for cryptographic signatures and X.509 certificates because the same data must always encode identically. BER allows multiple valid encodings for the same data.
You can decode X.509 certificates (PEM or DER), Certificate Signing Requests (CSR), RSA/EC/DSA private and public keys, PKCS#7 CMS structures, PKCS#12 bundles, and any arbitrary ASN.1 encoded data. Input can be PEM (BEGIN/END headers), Base64, or hexadecimal.
No. All decoding happens entirely in your browser using JavaScript. No data is transmitted to any server. Your certificates, private keys, and ASN.1 structures remain completely private on your device.
SEQUENCE (0x30), SET (0x31), INTEGER (0x02), BIT STRING (0x03), OCTET STRING (0x04), NULL (0x05), OBJECT IDENTIFIER (0x06), UTF8String (0x0C), PrintableString (0x13), IA5String (0x16), UTCTime (0x17), GeneralizedTime (0x18), and context-specific tags [0]–[3]. OIDs are resolved to human-readable names like rsaEncryption and commonName.

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