*.stai-alyasini.ac.id

Issued by R3

About this certificate

This digital certificate with serial number 04:bb:19:f6:c4:1d:66:ec:d9:39:b0:31:70:1e:dd:72:5f:24 was issued on by Let's Encrypt.

With 4 subject alternative names this certificate can be used to secure multiple fqdn's. 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=*.stai-alyasini.ac.id

Let's Encrypt

Organization: Let's Encrypt
Country: US

This certificate has expire since

Certificate Details

Serial Number (hex): 04:bb:19:f6:c4:1d:66:ec:d9:39:b0:31:70:1e:dd:72:5f:24
Serial Number (int): 412116458323860054550519825658861342318372
Serial Number lenght: 139 bits, 18 octets

SubjectKeyId: 8a:cd:ba:a4:0b:31:a2:e3:fa:30:39:8e:8f:76:80:c0:0e:e8:5c:b7
AuthorityKeyId: 14:2e:b3:17:b7:58:56:cb:ae:50:09:40:e6:1f:af:9d:8b:14:c2:c6

Fingerprint (sha1): 51:ca:78:56:30:62:d4:d8:aa:6c:50:24:a3:dd:cb:79:80:9a:3e:b8
Fingerprint (sha256): b2:97:67:48:98:85:eb:d8:88:1e:f0:26:14:4f:23:32:60:f6:4f:d3:eb:b0:42:38:c2:cd:f3:b8:93:4e:74:a8

Issuing Certificate URL: http://r3.i.lencr.org/

Revocation information

OCSP Server: http://r3.o.lencr.org

Check the revocation status for certificate *.stai-alyasini.ac.id

4

DNS Names

0

Email Addresses

0

IP Addresses

Advanced Certificate Properties

Tehnical certificate details for *.stai-alyasini.ac.id

Public Key Algorithm

RSA

Key Size

2048

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

*.stai-alyasini.ac.id
stai-alyasini.ac.id
www.pmb.stai-alyasini.ac.id
www.publikasi.stai-alyasini.ac.id

Other certificates including the domain name stai-alyasini.ac.id

(limited to 100 certificates)
stai-alyasini.ac.id
www.fi.stai-alyasini.ac.id
www.akademik.stai-alyasini.ac.id
*.stai-alyasini.ac.id
www.pmb.stai-alyasini.ac.id
stai-alyasini.ac.id
stai-alyasini.ac.id
stai-alyasini.ac.id
*.stai-alyasini.ac.id
stai-alyasini.ac.id
stai-alyasini.ac.id
daimuda.stai-alyasini.ac.id
www.drive.stai-alyasini.ac.id
stai-alyasini.ac.id
*.stai-alyasini.ac.id
www.pmb.stai-alyasini.ac.id
stai-alyasini.ac.id
www.lpm.stai-alyasini.ac.id
www.drive.stai-alyasini.ac.id
stai-alyasini.ac.id
stai-alyasini.ac.id
daimuda.stai-alyasini.ac.id
wisuda.stai-alyasini.ac.id
www.wisuda.stai-alyasini.ac.id
stai-alyasini.ac.id
stai-alyasini.ac.id
*.stai-alyasini.ac.id
mail.stai-alyasini.ac.id
sikami.stai-alyasini.ac.id
www.drive.stai-alyasini.ac.id
*.stai-alyasini.ac.id
stai-alyasini.ac.id
stai-alyasini.ac.id
stai-alyasini.ac.id
drive.stai-alyasini.ac.id
*.stai-alyasini.ac.id
www.feeder.stai-alyasini.ac.id

Certificate

The complete raw certificate details for *.stai-alyasini.ac.id in PEM and ASN.1 format.

Certificate (PEM)

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

Public Key (PEM)

-----BEGIN PUBLIC KEY-----
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAvGnxeH74f43ynOhkE8JK
bxgwIXBGMDCN6GTZdrvRuvNx8cchxPP44INaBmwtxl6EBJewSXTzvy/Ny8msKR46
VF9W8euLcueePcqd+E/IczERngginTiMp6Zhb8tLAM324PA76xFjO+WHK160gmhP
V2CD1pisMwP6o+rPUg2lsC2bkKeHR2YRVAXT6TQgBN7s3lUxopdUKT6971ienXd/
4qn8pF8C+qqyKpC9oD0OWhxVBeky4FY7MBF/lwlbEmfn6tyqdbRtuK7DzM5wI/Ny
ThDb5m9idUGy6nku2QmzI+rKJxcNDzm1YdIhp20tsuOrN2eWTPBvmmsMM6GjlXYq
WwIDAQAB
-----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 412116458323860054550519825658861342318372
 . . . . . . . . [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 'R3'
 . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . [c:0|t:23|false] UTCTime 2023-04-20 05:48:21 +0000 UTC
 . . . . . . . . . . . . [c:0|t:23|false] UTCTime 2023-07-19 05:48:20 +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:12|false] UTF8String '*.stai-alyasini.ac.id'
 . . . . . . . . [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 (2160 bits)
 . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . [c:0|t:2|false] INTEGER 23785043894772683529791979036987103981705083833758160933848611952786239062356216073541532700653205180149219415819273489287861592278110948834771510078145127513055904943774677652443088387238126003650206334543843828763787097259800144779183056061059722832703394681053008942439375737521745748474546320108863956907427349965403053040333245176872028776291020092812692320936025131410023876510218548309854608712222014830259193597439272009893273156706986165419757816085352079963553858177574459441902884329997284721235792935083987681640740298038257616630965843452409746671123140436161321509217922133088010519254402270888421894747
 . . . . . . . . . . . . . . . . . . . . [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)
							8acdbaa40b31a2e3fa30398e8f7680c00ee85cb7
 . . . . . . . . . . . . . . . . [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 142eb317b75856cbae500940e61faf9d8b14c2c6
 . . . . . . . . . . . . . . . . [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 (73 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://r3.o.lencr.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://r3.i.lencr.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 (110 bytes)
 . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:2|false] IA5String '*.stai-alyasini.ac.id'
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:2|false] IA5String 'stai-alyasini.ac.id'
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:2|false] IA5String 'www.pmb.stai-alyasini.ac.id'
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:2|false] IA5String 'www.publikasi.stai-alyasini.ac.id'
 . . . . . . . . . . . . . . . . [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)
							00f1007700b73efb24df9c4dba75f239c5ba58f46c5dfc42cf7a9f35c49e1d098125edb499000001879d6bd0320000040300483046022100cecc55d0a94dd821a606abbd94c95112b39a656ad58195ea7e73563f4cf723ed022100dea91af06eda7143fd2b88b4107fa722b9fb7e67d9edb8c18679b3481d4901130076007a328c54d8b72db620ea38e0521ee98416703213854d3bd22bc13a57a352eb52000001879d6bd04a0000040300473045022064c322b70b99463a9a9c2054361df8cde8d1cf1f8df93c90c07b5878e3c825bf022100eaf505a22707f6d2a8d24f13607b3e948a4b7498beee2ddc90f93df2ab28ad4b
 . . . . [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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