piwik.webkompleks.de

Issued by Let's Encrypt Authority X3

About this certificate

This digital certificate with serial number 03:72:2f:40:b4:e5:b2:ee:e7:36:c2:2c:19:5f:13:be:80:1e 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=piwik.webkompleks.de

Let's Encrypt

Organization: Let's Encrypt
Country: US

This certificate has expire since

Certificate Details

Serial Number (hex): 03:72:2f:40:b4:e5:b2:ee:e7:36:c2:2c:19:5f:13:be:80:1e
Serial Number (int): 300191857316100917070728359270728033271838
Serial Number lenght: 138 bits, 18 octets

SubjectKeyId: 43:fb:1e:19:c8:b4:75:dd:d4:2a:52:b1:ae:c8:4b:01:4c:51:18:d8
AuthorityKeyId: a8:4a:6a:63:04:7d:dd:ba:e6:d1:39:b7:a6:45:65:ef:f3:a8:ec:a1

Fingerprint (sha1): ce:80:f0:28:f0:42:a5:65:00:e5:c5:50:f6:83:c6:01:45:5c:ff:a6
Fingerprint (sha256): 57:38:87:1a:d4:a2:b3:97:53:92:6e:56:46:3e:a5:a6:d8:26:09:6f:3f:9c:59:50:28:7f:db:63:44:3b:9b:54

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 piwik.webkompleks.de

1

DNS Names

0

Email Addresses

0

IP Addresses

Advanced Certificate Properties

Tehnical certificate details for piwik.webkompleks.de

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

piwik.webkompleks.de

Other certificates including the domain name webkompleks.de

(limited to 100 certificates)

Certificate

The complete raw certificate details for piwik.webkompleks.de 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 300191857316100917070728359270728033271838
 . . . . . . . . [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 2019-01-11 01:01:06 +0000 UTC
 . . . . . . . . . . . . [c:0|t:23|false] UTCTime 2019-04-11 01:01:06 +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 'piwik.webkompleks.de'
 . . . . . . . . [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 795499827038673951058463914283762331078105172284462587051779860064741030596403310132323888578390132673007744830300562704989473493826411290406714392013374707489071156928797857803213666935948950271216634506754300516084188958790918466111406386892774909340659728598565876198424083036242402292996076141492983352404517055731438226982808557960935371487162986182432790219297344016569287055078445986642448363828076507682183134564974438976343871073451438811690988868597273161140834516785700670822191677504318929689694842474290773854150950929955065679217576647442175453184456472760631227417014364902827944202295192008292621934183624007261722613846539021474475495885565784367864786257251259608349946075214513501501583894158987170788872618053962699506355547252682003430231632397361843539068669456176764194973143307654028393534014016691247372218747027753705795657800485304696927594860564229435313523466468159218110638603147526826448541870480206870336472018086458935792778362042996319812239358686179812765709957587136809627297613298834552004779911073766847055585031990761937862954210658743746382063582409878433058905401716730920738861366927677800688391554543686504822967384328731799192279290028614650335410459063845581120007144646334787205554231191
 . . . . . . . . . . . . . . . . . . . . [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)
							43fb1e19c8b475ddd42a52b1aec84b014c5118d8
 . . . . . . . . . . . . . . . . [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 (24 bytes)
 . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:2|false] IA5String 'piwik.webkompleks.de'
 . . . . . . . . . . . . . . . . [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 (246 bytes)
 . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:4|false] OCTET STRING (243 bytes)
							00f1007600e2694bae26e8e94009e8861bb63b83d43ee7fe7488fba48f2893019dddf1dbfe000001683aa436a60000040300473045022100a584214d032bc2c4a2ab1779b4a34ee7c935626c43f62646681ac9f15d62dc190220397ff1fc2529ce72eb38d67eeaf980fa82ded149af7a4e99af4e543a87d0aee2007700293c519654c83965baaa50fc5807d4b76fbf587a2972dca4c30cf4e54547f478000001683aa434a20000040300483046022100f1f9cd7dc58c60bc0beb4bca2ad279d0e835c90e61fa6c0b23151a19fc308288022100991d449f5c0c6f352a206de2eb9ebd56bd5a1acf5cf556eb6463eb38ef0060fa
 . . . . [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)
		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