catherine.org

Issued by Let's Encrypt Authority X3

About this certificate

This digital certificate with serial number 03:fc:cf:0d:ef:c0:e1:3c:99:0f:1e:c1:3c:d1:82:9b:16:1f was issued on by Let's Encrypt.

This certificate has already expired and will cause a warning or error message in the browser it's still listed on this site to allow you to look back on previously issued certificates. If we have found any compliance issues with this certificate they will be shown below. I hope this certificate review is providing you the detailed information in a simple form you where looking for.


We have idenified some issues with this certificate:
  • Subscriber Certificate: commonName is deprecated. (BRs: 7.1.4.2.2)

Certificate Subject

CN=catherine.org

Let's Encrypt

Organization: Let's Encrypt
Country: US

This certificate has expire since

Certificate Details

Serial Number (hex): 03:fc:cf:0d:ef:c0:e1:3c:99:0f:1e:c1:3c:d1:82:9b:16:1f
Serial Number (int): 347363236817121281132140311357424481801759
Serial Number lenght: 138 bits, 18 octets

SubjectKeyId: 08:47:1d:56:0a:46:63:b7:c7:15:27:dd:c2:6b:61:f9:04:d5:f1:5a
AuthorityKeyId: a8:4a:6a:63:04:7d:dd:ba:e6:d1:39:b7:a6:45:65:ef:f3:a8:ec:a1

Fingerprint (sha1): 65:4a:e7:03:ba:8e:59:34:07:e8:7f:fa:af:3e:53:62:c9:1d:b8:2c
Fingerprint (sha256): 62:d5:e7:e4:41:ae:1d:84:6b:df:32:73:2b:85:8d:5e:c3:3f:13:8d:e5:98:10:f8:dc:d6:d4:ff:5b:cd:72:46

Issuing Certificate URL: http://cert.int-x3.letsencrypt.org/

Revocation information

OCSP Server: http://ocsp.int-x3.letsencrypt.org

Check the revocation status for certificate catherine.org

1

DNS Names

0

Email Addresses

0

IP Addresses

Advanced Certificate Properties

Tehnical certificate details for catherine.org

Public Key Algorithm

RSA

Key Size

4096

Signature Algorithm

SHA256 with RSA

Key Usage

Digital Signature
Key Encipherment

Extended Key Usages

Server Authentication
Client Authentication

Extensions

9 extensions
No unhandled critical extensions

CA Certificate

This is not a CA certificate

Subject Alternative Names

catherine.org

Other certificates including the domain name catherine.org

(limited to 100 certificates)
www.catherine.org
catherine.org
catherine.org
catherine.org
www.catherine.org
catherine.org
www.catherine.org
catherine.org
www.colzen.com
catherine.org
www.catherine.org
insectrepellant.organic
blynews.com
www.catherine.org
catherine.org
champagne.media

Certificate

The complete raw certificate details for catherine.org in PEM and ASN.1 format.

Certificate (PEM)

-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----

Public Key (PEM)

-----BEGIN PUBLIC KEY-----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-----END PUBLIC KEY-----

ASN.1 decoded

 [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . [c:2|t:0|true] OtherName 
 . . . . . . . . . . . . [c:0|t:2|false] INTEGER 2
 . . . . . . . . [c:0|t:2|false] INTEGER 347363236817121281132140311357424481801759
 . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 1.2.840.113549.1.1.11 (sha256WithRSAEncryption)
 . . . . . . . . . . . . [c:0|t:5|false] NULL 
 . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . [c:0|t:17|true] SET, SET OF 
 . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 2.5.4.6 (countryName)
 . . . . . . . . . . . . . . . . . . . . [c:0|t:19|false] PrintableString 'US'
 . . . . . . . . . . . . [c:0|t:17|true] SET, SET OF 
 . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 2.5.4.10 (organizationName)
 . . . . . . . . . . . . . . . . . . . . [c:0|t:19|false] PrintableString 'Let's Encrypt'
 . . . . . . . . . . . . [c:0|t:17|true] SET, SET OF 
 . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 2.5.4.3 (commonName)
 . . . . . . . . . . . . . . . . . . . . [c:0|t:19|false] PrintableString 'Let's Encrypt Authority X3'
 . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . [c:0|t:23|false] UTCTime 2019-09-29 01:06:08 +0000 UTC
 . . . . . . . . . . . . [c:0|t:23|false] UTCTime 2019-12-28 01:06:08 +0000 UTC
 . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . [c:0|t:17|true] SET, SET OF 
 . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 2.5.4.3 (commonName)
 . . . . . . . . . . . . . . . . . . . . [c:0|t:19|false] PrintableString 'catherine.org'
 . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 1.2.840.113549.1.1.1 (rsaEncryption)
 . . . . . . . . . . . . . . . . [c:0|t:5|false] NULL 
 . . . . . . . . . . . . [c:0|t:3|false] BIT STRING (4208 bits)
 . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . [c:0|t:2|false] INTEGER 779633851319253868346246884217499672503140072568423786157880311790894029519090455185998842447375635938102338422072663759282082191471686640637322490694069302215605568153631305582806038258455950539594743947454408755609163202930787385533323411287901161992580944020059324173528841414735992956242618671354122718311034229624577003716346173812129575180886729720355929580432233807973619381043932777739286334535988850360545684065452190022798065266866874923358364305493914900864902273165545525987890418289586896074106376652512349027640763168248885102400495648189199681421878109185879552720944681520272609299664665167886336303089598599930867593647345288318795721777877071681948382866940864343894754338931201639558472711405879238651976997491245693515390280006685845392754991260482175997016549827694057419441379134585096490369918183125035238647241875624395558425854747828759388651764657598703742079089025903702705817130934622583417266395597981408641071617601652494788855355198320286079352183426936527953991034814919018229389949372990570339373964102246781734790555365047874107865220765518705598220831061564051711650539025120358029855498550204219751867684249283190322654881916829278373612849759777744499588308200524317430042537758980298944915788559
 . . . . . . . . . . . . . . . . . . . . [c:0|t:2|false] INTEGER 65537

 . . . . . . . . [c:2|t:3|true] ORAddress 
 . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 2.5.29.15 (keyUsage)
 . . . . . . . . . . . . . . . . . . . . [c:0|t:1|false] BOOLEAN true
 . . . . . . . . . . . . . . . . . . . . [c:0|t:4|false] OCTET STRING (4 bytes)
 . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:3|false] BIT STRING (3 bits)
							05a0
 . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 2.5.29.37 (extKeyUsage)
 . . . . . . . . . . . . . . . . . . . . [c:0|t:4|false] OCTET STRING (22 bytes)
 . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 1.3.6.1.5.5.7.3.1 (serverAuth)
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 1.3.6.1.5.5.7.3.2 (clientAuth)
 . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 2.5.29.19 (basicConstraints)
 . . . . . . . . . . . . . . . . . . . . [c:0|t:1|false] BOOLEAN true
 . . . . . . . . . . . . . . . . . . . . [c:0|t:4|false] OCTET STRING (2 bytes)
 . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 2.5.29.14 (subjectKeyIdentifier)
 . . . . . . . . . . . . . . . . . . . . [c:0|t:4|false] OCTET STRING (22 bytes)
 . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:4|false] OCTET STRING (20 bytes)
							08471d560a4663b7c71527ddc26b61f904d5f15a
 . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 2.5.29.35 (authorityKeyIdentifier)
 . . . . . . . . . . . . . . . . . . . . [c:0|t:4|false] OCTET STRING (24 bytes)
 . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:0|false] OtherName a84a6a63047dddbae6d139b7a64565eff3a8eca1
 . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 1.3.6.1.5.5.7.1.1 (authorityInfoAccess)
 . . . . . . . . . . . . . . . . . . . . [c:0|t:4|false] OCTET STRING (99 bytes)
 . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 1.3.6.1.5.5.7.48.1 (ocsp)
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:6|false] IA5String 'http://ocsp.int-x3.letsencrypt.org'
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 1.3.6.1.5.5.7.48.2 (caIssuers)
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:6|false] IA5String 'http://cert.int-x3.letsencrypt.org/'
 . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 2.5.29.17 (subjectAltName)
 . . . . . . . . . . . . . . . . . . . . [c:0|t:4|false] OCTET STRING (17 bytes)
 . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:2|false] IA5String 'catherine.org'
 . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 2.5.29.32 (certificatePolicies)
 . . . . . . . . . . . . . . . . . . . . [c:0|t:4|false] OCTET STRING (69 bytes)
 . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 2.23.140.1.2.1 (Domain Validation Certificates Policy)
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 1.3.6.1.4.1.44947.1.1.1
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 1.3.6.1.5.5.7.2.1 (cps)
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:22|false] IA5String 'http://cps.letsencrypt.org'
 . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 1.3.6.1.4.1.11129.2.4.2
 . . . . . . . . . . . . . . . . . . . . [c:0|t:4|false] OCTET STRING (245 bytes)
 . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:4|false] OCTET STRING (242 bytes)
							00f00076006f5376ac31f03119d89900a45115ff77151c11d902c10029068db2089a37d9130000016d7ac49dd10000040300473045022100a4acba9f730fd5f2cac38fead41cc312eab3c71cbc86ee23216ec3731f144b2902207148e37fe41c978735457eb375eaaa35d3dd4cd17da2818efce3fe6ed1353b9b007600293c519654c83965baaa50fc5807d4b76fbf587a2972dca4c30cf4e54547f4780000016d7ac49ca50000040300473045022043b56375c5cf9c0de8c657fff557e3482596bd40182626b3ff5a6775446da59f022100c84047a11e6d3fac332c18c874adce1f99a461de103e2173afbf79f406bfafeb
 . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 1.2.840.113549.1.1.11 (sha256WithRSAEncryption)
 . . . . . . . . [c:0|t:5|false] NULL 
 . . . . [c:0|t:3|false] BIT STRING (2048 bits)
		004dbb2ed1d3c9bb86ff0e38e01c8d6492b31490322d1d5650932585121cda5ca4d1cbc01b1f4588248aed661c92615dc0da2d14167087f6cad2feba9724efed1b5ee4cd0122b4882a65e64756dfe2f29614d77612fbf4e3601ab024a9362ba5108a48312333bd5a939cf14a5be841639fe45ac5b524ef6b97846b07e6ea0a9acc7a5936b2820dc64c028fd0af7e836b10fb75d9d63a398718c59ecc26a95fa0c9ba01c112a49110616565ca87c6aed09da24a463c6016c3eb0c871170ffd5ab840a0afe76444597cdb62e9c033ac22771a59cbbd3d39829da7c62fb02dbe77a782780b27575c8128d605d4737647f81925a1356ee85be41e6216190450d200a4a