hetkliktmet.voka.be

Issued by Let's Encrypt Authority X3

About this certificate

This digital certificate with serial number 04:9e:c9:e2:36:28:27:1c:af:74:1c:05:4f:31:c4:03:b6:3b 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=hetkliktmet.voka.be

Let's Encrypt

Organization: Let's Encrypt
Country: US

This certificate has expire since

Certificate Details

Serial Number (hex): 04:9e:c9:e2:36:28:27:1c:af:74:1c:05:4f:31:c4:03:b6:3b
Serial Number (int): 402482107085223410466829233081648591124027
Serial Number lenght: 139 bits, 18 octets

SubjectKeyId: 43:fc:06:e8:71:22:9f:42:57:06:2e:ae:ee:23:3c:4e:94:00:5f:df
AuthorityKeyId: a8:4a:6a:63:04:7d:dd:ba:e6:d1:39:b7:a6:45:65:ef:f3:a8:ec:a1

Fingerprint (sha1): 48:3f:92:36:0f:b0:3f:17:4e:ad:55:34:cd:a6:84:fc:22:57:e3:03
Fingerprint (sha256): 7d:7d:ef:89:4a:25:88:c5:c6:10:f5:b5:b1:5e:19:1d:a3:ba:4a:35:6b:08:9a:05:d6:c6:3f:46:c6:d4:cd:4b

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 hetkliktmet.voka.be

1

DNS Names

0

Email Addresses

0

IP Addresses

Advanced Certificate Properties

Tehnical certificate details for hetkliktmet.voka.be

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

hetkliktmet.voka.be

Other certificates including the domain name voka.be

(limited to 100 certificates)

Certificate

The complete raw certificate details for hetkliktmet.voka.be 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 402482107085223410466829233081648591124027
 . . . . . . . . [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 2020-02-17 14:55:32 +0000 UTC
 . . . . . . . . . . . . [c:0|t:23|false] UTCTime 2020-05-17 14:55:32 +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 'hetkliktmet.voka.be'
 . . . . . . . . [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 828936755033242646623700508953658642413390998675027422191939305417413048892257124983973784846403817829358992619685800386564734355181640041884167757232244379517413859803474331576732282821249789661858485258850319586412018821416500041889767763926886295646649204077321751381904700778377501939077349234900037511904433562216498648508427608361452440133815512512634773533469479837517158812052946262245791827908774743188789306763458344011898845615924559253789776373459330863008012548592318720016220377321990153410334290706691618729497657704800079189201494312972038964533494769117778120657730398197373827677066909633392625806763862942538846823940545221445956023327746520032301868413288814441958623153148421480508635407506269969602439763978811175685806958340575777785148883963808518443690429556269561113829380331107465381593250485650046890654053581361734456287171681254256192452080095476994783806400796302503509213816422466616652870700410423939929783410878287284403833674374524322022990310349427648603138312066984272748231153284228952952862734751110815481300311175884649315659169499312894265244093801968382559715686727021195144357722013019781101447407086575392510034362496872095778008298454545014665854017603373820738803234301593231235660851157
 . . . . . . . . . . . . . . . . . . . . [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)
							43fc06e871229f4257062eaeee233c4e94005fdf
 . . . . . . . . . . . . . . . . [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 (23 bytes)
 . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:2|false] IA5String 'hetkliktmet.voka.be'
 . . . . . . . . . . . . . . . . [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 (244 bytes)
 . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:4|false] OCTET STRING (241 bytes)
							00ef007500f095a459f200d18240102d2f93888ead4bfe1d47e399e1d034a6b0a8aa8eb2730000017053dca09e000004030046304402200de861b6b6b37764d1b2078d08f1e1169b028c409815f1643528a83d06414fe402205c7b7013f0868a21dd40ec6d2024ffc2087dffcc4eb366b752eba61803d63564007600b21e05cc8ba2cd8a204e8766f92bb98a2520676bdafa70e7b249532def8b905e0000017053dca08d0000040300473045022100e497f2ad6e5d9518820d192e33f52913411ff4d034bc9e2b4e50393c8e5aac8e022051d696f1710fc16aacdaa5e138ae70875bb3446b0fa52d7b3e2162431f11a949
 . . . . [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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