ASN.1 Decoder

See the ASN.1 structure of any DER data, with tags, lengths, object identifiers and strings decoded into a collapsible tree.

PEM, Base64 & hex
OID names
Nested strings expanded
Nothing uploaded

Paste PEM, Base64 or hex DER

Found: 3 certificates

#1 Certificate

www.example.com

SEQUENCE (699 B)
- SEQUENCE (609 B)
  - [0] (3 B)
    INTEGER (1 B) 2
  - INTEGER (9 B) 72-bit: 04d2a1b3c4d5e6f708…
  - SEQUENCE (10 B)
    OBJECT IDENTIFIER (8 B) 1.2.840.10045.4.3.2 (ecdsa-with-SHA256)
  - SEQUENCE (83 B)
    SET (11 B)
    SEQUENCE (9 B)
    OBJECT IDENTIFIER (3 B) 2.5.4.6 (Country)
    PrintableString (2 B) "GB"
    SET (32 B)
    SEQUENCE (30 B)
    OBJECT IDENTIFIER (3 B) 2.5.4.10 (Organization)
    UTF8String (23 B) "Digital ToolPad Example"
    SET (34 B)
    SEQUENCE (32 B)
    OBJECT IDENTIFIER (3 B) 2.5.4.3 (Common name)
    UTF8String (25 B) "Example TLS Issuing CA E1"
  - SEQUENCE (30 B)
    UTCTime (13 B) 261001000000Z → 2026-10-01T00:00:00Z
    UTCTime (13 B) 311001000000Z → 2031-10-01T00:00:00Z
  - SEQUENCE (26 B)
    SET (24 B)
    SEQUENCE (22 B)
    OBJECT IDENTIFIER (3 B) 2.5.4.3 (Common name)
    UTF8String (15 B) "www.example.com"
  - SEQUENCE (89 B)
    SEQUENCE (19 B)
    OBJECT IDENTIFIER (7 B) 1.2.840.10045.2.1 (EC)
    OBJECT IDENTIFIER (8 B) 1.2.840.10045.3.1.7 (prime256v1)
    BIT STRING (66 B) 00 04 13 29 64 7E 36 0E EC 3B 82 25 0E B2 44 F4 42 66 2C A4 25 52 38 38 48 D2 6A 87 7D 08 C0 4E … (66 bytes)
  - [3] (341 B)
    SEQUENCE (337 B)
    SEQUENCE (12 B)
    OBJECT IDENTIFIER (3 B) 2.5.29.19 (Basic Constraints)
    BOOLEAN (1 B) TRUE
    OCTET STRING (2 B) encapsulates
    SEQUENCE (0 B)
    SEQUENCE (14 B)
    OBJECT IDENTIFIER (3 B) 2.5.29.15 (Key Usage)
    BOOLEAN (1 B) TRUE
    OCTET STRING (4 B) encapsulates
    BIT STRING (2 B) 07 80
    SEQUENCE (19 B)
    OBJECT IDENTIFIER (3 B) 2.5.29.37 (Extended Key Usage)
    OCTET STRING (12 B) encapsulates
    SEQUENCE (10 B)
    OBJECT IDENTIFIER (8 B) 1.3.6.1.5.5.7.3.1 (TLS server authentication)
    SEQUENCE (56 B)
    OBJECT IDENTIFIER (3 B) 2.5.29.17 (Subject Alternative Name)
    OCTET STRING (49 B) encapsulates
    SEQUENCE (47 B)
    [2] (15 B) "www.example.com"
    [2] (11 B) "example.com"
    [2] (15 B) "api.example.com"
    SEQUENCE (29 B)
    OBJECT IDENTIFIER (3 B) 2.5.29.14 (Subject Key Identifier)
    OCTET STRING (22 B) encapsulates
    OCTET STRING (20 B) C9 2D 54 FC 59 B8 81 D5 08 63 C7 09 CB ED 05 43 C0 14 06 99
    SEQUENCE (31 B)
    OBJECT IDENTIFIER (3 B) 2.5.29.35 (Authority Key Identifier)
    OCTET STRING (24 B) encapsulates
    SEQUENCE (22 B)
    [0] (20 B) AD A8 BA C9 B2 99 02 5B 24 40 64 9F 8D E3 A5 C8 A8 C1 76 54
    SEQUENCE (93 B)
    OBJECT IDENTIFIER (8 B) 1.3.6.1.5.5.7.1.1 (Authority Information Access)
    OCTET STRING (81 B) encapsulates
    SEQUENCE (79 B)
    SEQUENCE (35 B)
    OBJECT IDENTIFIER (8 B) 1.3.6.1.5.5.7.48.1 (OCSP)
    [6] (23 B) "http://ocsp.example.com"
    SEQUENCE (40 B)
    OBJECT IDENTIFIER (8 B) 1.3.6.1.5.5.7.48.2 (CA issuers)
    [6] (28 B) "http://ca.example.com/e1.crt"
    SEQUENCE (46 B)
    OBJECT IDENTIFIER (3 B) 2.5.29.31 (CRL Distribution Points)
    OCTET STRING (39 B) encapsulates
    SEQUENCE (37 B)
    SEQUENCE (35 B)
    [0] (33 B)
    [0] (31 B)
    [6] (29 B) "http://crl.example.com/e1.crl"
    SEQUENCE (19 B)
    OBJECT IDENTIFIER (3 B) 2.5.29.32 (Certificate Policies)
    OCTET STRING (12 B) encapsulates
    SEQUENCE (10 B)
    SEQUENCE (8 B)
    OBJECT IDENTIFIER (6 B) 2.23.140.1.2.1 (CA/Browser Forum domain validated)
- SEQUENCE (10 B)
  - OBJECT IDENTIFIER (8 B) 1.2.840.10045.4.3.2 (ecdsa-with-SHA256)
- BIT STRING (72 B) encapsulates
  - SEQUENCE (69 B)
    INTEGER (32 B) 256-bit: 24edd96124e721aa86fcc634057f460700c5bc949de9cb01…
    INTEGER (33 B) 264-bit: 00fcf6f200833e132e389341c0d5be53047e7275c77c5485…

#2 CA certificate

Example TLS Issuing CA E1

SEQUENCE (572 B)
- SEQUENCE (450 B)
  - [0] (3 B)
    INTEGER (1 B) 2
  - INTEGER (8 B) 6493767353929559553
  - SEQUENCE (10 B)
    OBJECT IDENTIFIER (8 B) 1.2.840.10045.4.3.3 (ecdsa-with-SHA384)
  - SEQUENCE (76 B)
    SET (11 B)
    SEQUENCE (9 B)
    OBJECT IDENTIFIER (3 B) 2.5.4.6 (Country)
    PrintableString (2 B) "GB"
    SET (32 B)
    SEQUENCE (30 B)
    OBJECT IDENTIFIER (3 B) 2.5.4.10 (Organization)
    UTF8String (23 B) "Digital ToolPad Example"
    SET (27 B)
    SEQUENCE (25 B)
    OBJECT IDENTIFIER (3 B) 2.5.4.3 (Common name)
    UTF8String (18 B) "Example Root CA R1"
  - SEQUENCE (30 B)
    UTCTime (13 B) 260101000000Z → 2026-01-01T00:00:00Z
    UTCTime (13 B) 360101000000Z → 2036-01-01T00:00:00Z
  - SEQUENCE (83 B)
    SET (11 B)
    SEQUENCE (9 B)
    OBJECT IDENTIFIER (3 B) 2.5.4.6 (Country)
    PrintableString (2 B) "GB"
    SET (32 B)
    SEQUENCE (30 B)
    OBJECT IDENTIFIER (3 B) 2.5.4.10 (Organization)
    UTF8String (23 B) "Digital ToolPad Example"
    SET (34 B)
    SEQUENCE (32 B)
    OBJECT IDENTIFIER (3 B) 2.5.4.3 (Common name)
    UTF8String (25 B) "Example TLS Issuing CA E1"
  - SEQUENCE (89 B)
    SEQUENCE (19 B)
    OBJECT IDENTIFIER (7 B) 1.2.840.10045.2.1 (EC)
    OBJECT IDENTIFIER (8 B) 1.2.840.10045.3.1.7 (prime256v1)
    BIT STRING (66 B) 00 04 32 53 B8 04 AB EB 6D 12 12 F8 FF 21 C4 C3 F1 B9 A1 34 81 66 64 1C AE 9D 2B 27 97 77 5C 69 … (66 bytes)
  - [3] (134 B)
    SEQUENCE (131 B)
    SEQUENCE (18 B)
    OBJECT IDENTIFIER (3 B) 2.5.29.19 (Basic Constraints)
    BOOLEAN (1 B) TRUE
    OCTET STRING (8 B) encapsulates
    SEQUENCE (6 B)
    BOOLEAN (1 B) TRUE
    INTEGER (1 B) 0
    SEQUENCE (14 B)
    OBJECT IDENTIFIER (3 B) 2.5.29.15 (Key Usage)
    BOOLEAN (1 B) TRUE
    OCTET STRING (4 B) encapsulates
    BIT STRING (2 B) 01 86
    SEQUENCE (29 B)
    OBJECT IDENTIFIER (3 B) 2.5.29.37 (Extended Key Usage)
    OCTET STRING (22 B) encapsulates
    SEQUENCE (20 B)
    OBJECT IDENTIFIER (8 B) 1.3.6.1.5.5.7.3.1 (TLS server authentication)
    OBJECT IDENTIFIER (8 B) 1.3.6.1.5.5.7.3.2 (TLS client authentication)
    SEQUENCE (29 B)
    OBJECT IDENTIFIER (3 B) 2.5.29.14 (Subject Key Identifier)
    OCTET STRING (22 B) encapsulates
    OCTET STRING (20 B) AD A8 BA C9 B2 99 02 5B 24 40 64 9F 8D E3 A5 C8 A8 C1 76 54
    SEQUENCE (31 B)
    OBJECT IDENTIFIER (3 B) 2.5.29.35 (Authority Key Identifier)
    OCTET STRING (24 B) encapsulates
    SEQUENCE (22 B)
    [0] (20 B) ED AD 1E F1 5A DA 94 57 B3 78 85 2B 00 84 16 BB E9 D1 06 6F
- SEQUENCE (10 B)
  - OBJECT IDENTIFIER (8 B) 1.2.840.10045.4.3.3 (ecdsa-with-SHA384)
- BIT STRING (104 B) encapsulates
  - SEQUENCE (101 B)
    INTEGER (48 B) 384-bit: 34783d2f7d69038e6092f36a619ef0c0d38cdbf022eb6e95…
    INTEGER (49 B) 392-bit: 00fe86691fe7dba24b3589fbd09b230e974d1d157162b5bb…

#3 CA certificate

Example Root CA R1

SEQUENCE (571 B)
- SEQUENCE (448 B)
  - [0] (3 B)
    INTEGER (1 B) 2
  - INTEGER (20 B) 160-bit: 3c4f38ebfda19afdd065acc8008405497bb5261c…
  - SEQUENCE (10 B)
    OBJECT IDENTIFIER (8 B) 1.2.840.10045.4.3.3 (ecdsa-with-SHA384)
  - SEQUENCE (76 B)
    SET (11 B)
    SEQUENCE (9 B)
    OBJECT IDENTIFIER (3 B) 2.5.4.6 (Country)
    PrintableString (2 B) "GB"
    SET (32 B)
    SEQUENCE (30 B)
    OBJECT IDENTIFIER (3 B) 2.5.4.10 (Organization)
    UTF8String (23 B) "Digital ToolPad Example"
    SET (27 B)
    SEQUENCE (25 B)
    OBJECT IDENTIFIER (3 B) 2.5.4.3 (Common name)
    UTF8String (18 B) "Example Root CA R1"
  - SEQUENCE (30 B)
    UTCTime (13 B) 260101000000Z → 2026-01-01T00:00:00Z
    UTCTime (13 B) 460101000000Z → 2046-01-01T00:00:00Z
  - SEQUENCE (76 B)
    SET (11 B)
    SEQUENCE (9 B)
    OBJECT IDENTIFIER (3 B) 2.5.4.6 (Country)
    PrintableString (2 B) "GB"
    SET (32 B)
    SEQUENCE (30 B)
    OBJECT IDENTIFIER (3 B) 2.5.4.10 (Organization)
    UTF8String (23 B) "Digital ToolPad Example"
    SET (27 B)
    SEQUENCE (25 B)
    OBJECT IDENTIFIER (3 B) 2.5.4.3 (Common name)
    UTF8String (18 B) "Example Root CA R1"
  - SEQUENCE (118 B)
    SEQUENCE (16 B)
    OBJECT IDENTIFIER (7 B) 1.2.840.10045.2.1 (EC)
    OBJECT IDENTIFIER (5 B) 1.3.132.0.34 (secp384r1)
    BIT STRING (98 B) 00 04 79 67 8D D2 65 11 1A 74 23 36 50 71 AE 4F 5F C2 60 97 EF 12 69 9F BD 50 7E D5 3A FE FE 74 … (98 bytes)
  - [3] (99 B)
    SEQUENCE (97 B)
    SEQUENCE (31 B)
    OBJECT IDENTIFIER (3 B) 2.5.29.35 (Authority Key Identifier)
    OCTET STRING (24 B) encapsulates
    SEQUENCE (22 B)
    [0] (20 B) ED AD 1E F1 5A DA 94 57 B3 78 85 2B 00 84 16 BB E9 D1 06 6F
    SEQUENCE (15 B)
    OBJECT IDENTIFIER (3 B) 2.5.29.19 (Basic Constraints)
    BOOLEAN (1 B) TRUE
    OCTET STRING (5 B) encapsulates
    SEQUENCE (3 B)
    BOOLEAN (1 B) TRUE
    SEQUENCE (14 B)
    OBJECT IDENTIFIER (3 B) 2.5.29.15 (Key Usage)
    BOOLEAN (1 B) TRUE
    OCTET STRING (4 B) encapsulates
    BIT STRING (2 B) 01 06
    SEQUENCE (29 B)
    OBJECT IDENTIFIER (3 B) 2.5.29.14 (Subject Key Identifier)
    OCTET STRING (22 B) encapsulates
    OCTET STRING (20 B) ED AD 1E F1 5A DA 94 57 B3 78 85 2B 00 84 16 BB E9 D1 06 6F
- SEQUENCE (10 B)
  - OBJECT IDENTIFIER (8 B) 1.2.840.10045.4.3.3 (ecdsa-with-SHA384)
- BIT STRING (105 B) encapsulates
  - SEQUENCE (102 B)
    INTEGER (49 B) 392-bit: 00aa1b1c49b87c71c6a62a12fc3a277e5f4e924800f541b2…
    INTEGER (49 B) 392-bit: 00b5638f94dd61aff64ec9110003e234bbe1078bec3ad7ee…

What is an ASN.1 decoder?

ASN.1 (Abstract Syntax Notation One) describes the structure of certificates, keys, signatures, LDAP and SNMP messages and many telecom protocols. DER is its binary encoding: every value is a tag, a length and the contents. An ASN.1 decoder walks that encoding and shows it as a tree: SEQUENCE and SET containers, INTEGERs, OBJECT IDENTIFIERs with their registered names, strings and times. This decoder accepts PEM, Base64 or hex, expands OCTET STRINGs and BIT STRINGs that wrap more DER (as certificate extensions do), and also decodes recognised certificates, CSRs and keys into readable fields.

How to decode ASN.1

Paste PEM, Base64 or hex (spaces and colons are fine), or open a binary file.
Expand and collapse SEQUENCE and SET nodes in the tree.
Read OIDs by name and strings and times in plain text.
Switch to Details for certificates and CSRs, or PEM & DER to export.

The OpenSSL equivalents

Prefer the command line? These OpenSSL commands do the same job on your own machine.

ASN.1 dump of a PEM file: openssl asn1parse -in cert.pem -i
ASN.1 dump of a DER file: openssl asn1parse -inform der -in data.der -i

Why use this ASN.1 decoder

Readable OIDsHundreds of object identifiers for algorithms, curves, extensions and name attributes are labelled.
Encapsulated data expandedDER hidden inside OCTET STRING and BIT STRING values is decoded too.
Safe on bad inputTruncated lengths, extra bytes and deep nesting are reported instead of crashing.
Nothing is uploadedDecoding and signature checks run in your browser with the Web Crypto API. Certificates and CSRs never reach a server, which matters for internal hosts and unreleased domains.

Common uses

Debug encoders. Check the DER your code produces.
Learn X.509. See how a certificate is structured field by field.
Signatures. Inspect ECDSA (r, s) and PKCS#7 structures.
Protocols. Decode DER from LDAP, SNMP or smart cards.

More developer tools: the JWT decoder, Base64 decoder, hash generator and subnet calculator.

Example: the structure of a certificate

The sample certificate opens as SEQUENCE → tbsCertificate, signatureAlgorithm (1.2.840.10045.4.3.2, ecdsa-with-SHA256) and a BIT STRING holding the signature, itself a SEQUENCE of two INTEGERs.

What to expect from the result

BER indefinite lengths are supported; other non-DER encodings (PER, XER) are not. Very large structures show the first 3,000 nodes.

ASN.1 Decoder questions

How do I decode ASN.1 online?

Paste the data as PEM, Base64 or hex, or open the binary file. The tree appears instantly; nothing is uploaded.

What is the difference between ASN.1 and DER?

ASN.1 is the schema language that describes structures. DER (Distinguished Encoding Rules) is one way to encode them as bytes, used by X.509 certificates.

Can it decode hex?

Yes. Hex with or without spaces or colons works, as long as it is DER starting with 30 (a SEQUENCE).

What does “encapsulates” mean?

Some OCTET STRING and BIT STRING values contain another DER structure, such as certificate extensions and public keys. The decoder shows those nested structures.

Is it safe to paste my certificate here?

Yes. Certificates and CSRs contain only public information, and this tool decodes them in your browser without sending anything to a server. Never paste a private key into any website; if you do, this tool refuses to decode it.

ASN.1 Decoder

www.example.com

Example TLS Issuing CA E1

Example Root CA R1

What is an ASN.1 decoder?

How to decode ASN.1

The OpenSSL equivalents

Why use this ASN.1 decoder

Common uses

Example: the structure of a certificate

What to expect from the result

ASN.1 Decoder questions

100% private — your data never leaves your browser

No server, no uploads

Works offline

Verify it yourself

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