phosai.com

Issued by Let's Encrypt Authority X3

About this certificate

This digital certificate with serial number 03:b3:ef:7b:68:4f:fc:a0:ec:8c:c2:7d:29:3f:c6:2e:0b:b8 was issued on by Let's Encrypt.

With 2 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=phosai.com

Let's Encrypt

Organization: Let's Encrypt
Country: US

This certificate has expire since

Certificate Details

Serial Number (hex): 03:b3:ef:7b:68:4f:fc:a0:ec:8c:c2:7d:29:3f:c6:2e:0b:b8
Serial Number (int): 322565727733342727963319844965255635405752
Serial Number lenght: 138 bits, 18 octets

SubjectKeyId: 08:5c:77:ac:80:3b:72:a9:9f:9b:51:12:00:0f:9d:66:80:95:f1:08
AuthorityKeyId: a8:4a:6a:63:04:7d:dd:ba:e6:d1:39:b7:a6:45:65:ef:f3:a8:ec:a1

Fingerprint (sha1): 4e:97:41:9e:08:e3:7b:a9:60:79:8d:68:70:b5:65:71:94:2f:18:67
Fingerprint (sha256): 2f:8a:85:a4:84:6d:cd:58:07:20:63:20:2d:ec:39:6b:67:a8:4e:e3:65:b5:f5:34:c8:fd:84:74:ab:4e:1d:2d

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 phosai.com

2

DNS Names

0

Email Addresses

0

IP Addresses

Advanced Certificate Properties

Tehnical certificate details for phosai.com

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

phosai.com
www.phosai.com

Other certificates including the domain name phosai.com

(limited to 100 certificates)

Certificate

The complete raw certificate details for phosai.com 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 322565727733342727963319844965255635405752
 . . . . . . . . [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 2019-09-28 16:07:46 +0000 UTC
 . . . . . . . . . . . . [c:0|t:23|false] UTCTime 2019-12-27 16:07:46 +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 'phosai.com'
 . . . . . . . . [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 689695870303342022114247510878087228270509370182418232322245189093100400839266988701622894751677684164389715817896197199194723642838373407623030602144308653920484549632889103027970281395690182301704413165278548154026100645617830874273132761432385250101271986123710510411535265943251454077781467844540262288313085640256056628349083795655209832838446397671023167192468602843252824199025130113150811207962125641130428055314648059365079410538237813131315795554714531616065194549574093737558343867296989183344041570827554033836377533308108039429490041216821263017420392206750660340585940379168916550074965330583589130657343538447104238652762776786199203155716515383083433511135464353342030728138809166044961563829147936629401933802979165119755670710784752834966138115324971440597786598864199968557846261331605305086248085983182264112483110852798327790572278772836649068078700160651662740283985852335890927137483544963962742682962928879698705534270988856885534868749392505952091684615640992582602143260008997317084439368046143379169040737081503145925930397326543164278118562357261884678157581728573638327233710888157695820766163865970102399143440287660932239011390673592604607215185744626497302660388905494256387396940481869413774426596613
 . . . . . . . . . . . . . . . . . . . . [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)
							085c77ac803b72a99f9b5112000f9d668095f108
 . . . . . . . . . . . . . . . . [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 (30 bytes)
 . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:2|false] IA5String 'phosai.com'
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:2|false] IA5String 'www.phosai.com'
 . . . . . . . . . . . . . . . . [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 (247 bytes)
 . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:4|false] OCTET STRING (244 bytes)
							00f2007700747eda8331ad331091219cce254f4270c2bffd5e422008c6373579e6107bcc560000016d78d7b7d7000004030048304602210093991e2b7e0b687fdec6ec499a742e32f6fa8d5b89faaf0428139ed392a81e21022100f0c01cf70cb586a8f0fa7971fb97c30cfe79f0cc03991314853387f0f9a752d7007700293c519654c83965baaa50fc5807d4b76fbf587a2972dca4c30cf4e54547f4780000016d78d7b9ea0000040300483046022100c28bd41e18932455781008b344da9efd3c1f726213f799551e10fca5e56ffce0022100d0cc1b43940455673692a3df1598e850d54063887909cb36bb56b7326644466f
 . . . . [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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