ASN.1 Decoder Online | DER and PEM Parser

ASN.1 decoder for DER and PEM: view certificates, keys, CSRs and PKCS #7 as a tree of tags, lengths, OIDs and values. Runs in your browser, nothing uploaded. Designed specifically for developers and professionals, this free online decoder runs entirely in your browser to process tasks quickly and securely. Enjoy unlimited usage with no data tracking and no registration required.

Also known as: asn1 decoder · asn.1 decoder online · der decoder online · asn1 parser · pem decoder · decode der certificate · asn1 viewer · ber decoder · asn.1 der parser · x509 asn1 parser

encoding and decoding tools

ssl and security tools

decoders

PEM or DER Input

Input as

ASN.1 Structure

The decoded ASN.1 tree will appear here, with every tag, length, OID and value you can expand and filter.

About ASN.1 Decoder

This ASN.1 decoder parses DER and BER bytes from a PEM file, hex or Base64 into an indented tree of tags, lengths and values. Developers use it to debug X.509 certificates, CSRs, private and public keys, PKCS #7 and CMS signatures, and any other ASN.1 structure when a TLS library or signature check rejects a file without saying why.

Key Features

Decodes every X.690 tag class and form, including multi-byte tag numbers and BER indefinite-length encoding
Finds DER wrapped inside BIT STRING and OCTET STRING, so public keys and certificate extensions expand in place
Names 80 common OIDs, from sha256WithRSAEncryption and ecPublicKey to subjectAltName and serverAuth
Shows INTEGER, OID, UTCTime and GeneralizedTime values decoded, and strings as UTF-8, BMP or ASCII text
Flags DER rule breaks such as long-form lengths, redundant INTEGER bytes and non-canonical BOOLEAN values
Reports truncated data with the byte offset, and decodes several PEM blocks from one paste, such as a full chain

Use Cases

Find out why Java, Go or OpenSSL rejects a certificate or private key that looks fine in a text editor
Check the extensions, SAN entries and key usage bits in a CSR before sending it to DigiCert or Let's Encrypt
Inspect a PKCS #8 or SEC1 EC private key to confirm the curve before loading it into AWS KMS or Vault
Read the SignerInfo in a PKCS #7 or CMS signature from a code-signing or S/MIME pipeline
Compare the DER your own encoder writes against a reference file byte by byte, with offsets
Decode an SNMP, LDAP or Kerberos message captured in Wireshark while troubleshooting on-premises auth

Supported Formats

PEM: CERTIFICATE, CERTIFICATE REQUEST, PRIVATE KEY, PUBLIC KEY, EC PRIVATE KEY, RSA PRIVATE KEY, PKCS7, X509 CRL

DER as hex, with spaces, colons or 0x prefixes

DER as Base64 or base64url

.der, .cer, .crt, .pem, .csr, .key, .p7b, .p8 and .crl files

BER with indefinite lengths

Related Keywords

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der decoder online

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asn1 viewer

ber decoder

asn.1 der parser

x509 asn1 parser

What is the difference between ASN.1, DER and PEM?

ASN.1 is the schema language that defines structures like an X.509 certificate. DER is one way to encode those structures as bytes: every value is a tag, a length and content, with exactly one valid encoding so signatures stay stable. BER is the looser parent of DER that also allows indefinite lengths. PEM is simply DER in Base64 between -----BEGIN and -----END lines, so it can be pasted into email or a config file.

Privacy & Security

All processing happens locally in your browser. Your data never leaves your computer, ensuring complete privacy and security.

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Frequently asked questions

What is ASN.1 Decoder Online used for?

ASN.1 decoder for DER and PEM: view certificates, keys, CSRs and PKCS #7 as a tree of tags, lengths, OIDs and values. Runs in your browser, nothing uploaded.

Is ASN.1 Decoder Online free to use?

Yes. ASN.1 Decoder Online is completely free with no usage limits, and there is no paid tier required to use it.

Do I need an account to use ASN.1 Decoder Online?

No. ASN.1 Decoder Online works immediately in your browser with no signup, login, or email address required.

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