o2bhealthy.co.nz
Issued by Let's Encrypt Authority X3
About this certificate
This digital certificate with serial number 03:68:79:ff:c8:5d:7d:9c:a7:bd:56:15:17:48:ce:36:b5:86 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=o2bhealthy.co.nz
Let's Encrypt
Organization:
Let's Encrypt
Country:
US
This certificate has expire since
Certificate Details
Serial Number (hex): 03:68:79:ff:c8:5d:7d:9c:a7:bd:56:15:17:48:ce:36:b5:86Serial Number (int): 296888388642136256196673329971576543032710
Serial Number lenght: 138 bits, 18 octets
SubjectKeyId: 26:15:47:ca:1b:55:6c:5b:73:75:45:fc:f4:84:be:76:be:40:c7:c6
AuthorityKeyId: a8:4a:6a:63:04:7d:dd:ba:e6:d1:39:b7:a6:45:65:ef:f3:a8:ec:a1
Fingerprint (sha1): 15:69:9f:0c:49:da:f4:bc:b9:87:ad:8f:f4:b6:3c:92:80:2f:6a:0e
Fingerprint (sha256): f8:96:83:d8:93:bf:4f:06:29:74:e6:f8:a9:db:1e:72:d9:3d:f4:96:2f:ab:2e:83:13:eb:c8:eb:81:b3:be:51
Issuing Certificate URL: http://cert.int-x3.letsencrypt.org/
Revocation information
OCSP Server: http://ocsp.int-x3.letsencrypt.orgCheck the revocation status for certificate o2bhealthy.co.nz
4
DNS Names
0
Email Addresses
0
IP Addresses
Advanced Certificate Properties
Tehnical certificate details for o2bhealthy.co.nz
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
o2bhealthy.co.nz
o2bhealthy.nz
www.o2bhealthy.co.nz
www.o2bhealthy.nz
o2bhealthy.nz
www.o2bhealthy.co.nz
www.o2bhealthy.nz
Other certificates including the domain name o2bhealthy.co.nz
(limited to 100 certificates)
o2bhealthy.co.nz
o2bhealthy.co.nz
o2bhealthy.nz
o2bhealthy.nz
www.o2bhealthy.co.nz
o2bhealthy.co.nz
o2bhealthy.nz
o2bhealthy.co.nz
o2bhealthy.co.nz
*.02b.co.nz
o2bhealthy.nz
o2bhealthy.co.nz
o2bhealthy.co.nz
o2bhealthy.co.nz
*.02b.co.nz
o2bhealthy.nz
o2bhealthy.co.nz
o2bhealthy.co.nz
o2bhealthy.co.nz
o2bhealthy.co.nz
o2bhealthy.co.nz
o2bhealthy.co.nz
*.02b.co.nz
www.o2bhealthy.co.nz
o2bhealthy.nz
o2bhealthy.nz
o2bhealthy.co.nz
o2bhealthy.co.nz
o2bhealthy.nz
*.02b.co.nz
o2bhealthy.nz
*.02b.co.nz
o2bhealthy.co.nz
o2bhealthy.co.nz
o2bhealthy.co.nz
o2bhealthy.nz
o2bhealthy.nz
www.o2bhealthy.co.nz
o2bhealthy.co.nz
o2bhealthy.nz
o2bhealthy.co.nz
o2bhealthy.co.nz
*.02b.co.nz
o2bhealthy.nz
o2bhealthy.co.nz
o2bhealthy.co.nz
o2bhealthy.co.nz
*.02b.co.nz
o2bhealthy.nz
o2bhealthy.co.nz
o2bhealthy.co.nz
o2bhealthy.co.nz
o2bhealthy.co.nz
o2bhealthy.co.nz
o2bhealthy.co.nz
*.02b.co.nz
www.o2bhealthy.co.nz
o2bhealthy.nz
o2bhealthy.nz
o2bhealthy.co.nz
o2bhealthy.co.nz
o2bhealthy.nz
*.02b.co.nz
o2bhealthy.nz
*.02b.co.nz
o2bhealthy.co.nz
o2bhealthy.co.nz
Certificate
The complete raw certificate details for o2bhealthy.co.nz in PEM and ASN.1 format.
Certificate (PEM)
-----BEGIN CERTIFICATE----- MIIFjzCCBHegAwIBAgISA2h5/8hdfZynvVYVF0jONrWGMA0GCSqGSIb3DQEBCwUA MEoxCzAJBgNVBAYTAlVTMRYwFAYDVQQKEw1MZXQncyBFbmNyeXB0MSMwIQYDVQQD ExpMZXQncyBFbmNyeXB0IEF1dGhvcml0eSBYMzAeFw0xOTExMjYxNTAxNDFaFw0y MDAyMjQxNTAxNDFaMBsxGTAXBgNVBAMTEG8yYmhlYWx0aHkuY28ubnowggEiMA0G CSqGSIb3DQEBAQUAA4IBDwAwggEKAoIBAQDCnX3vSECUH9epv112pzrLd5KzJJQ4 jfiD0igp9FFZiX/fg6vmfet/OWyjxlpgvm56h3OkmXdlaLVFkaYZ1EWA2hsgNllq 2lWVO9egissHg3Q65KQg+jj8qXhAk9T9C65E0o+GtpvVu/U86Ooi7IKo67+Cz0yy 7AYPGSgN6/hC3vJ3pdVQ7EY3eDF4VBsi3zpF4fKM2lgpfEx1dwLTOwqMn7JQYeP1 zQbreR/mynEtBghjFeyovz9KzrQ/5WPrpGKyQGu56vR9ZyQvVNUkxtUaTkefj30x P6VSFliVStkJ5xjrNsUB40vS5Em8GtBwsx0c5QsJsdX3Bmjwj/l5K6pnAgMBAAGj ggKcMIICmDAOBgNVHQ8BAf8EBAMCBaAwHQYDVR0lBBYwFAYIKwYBBQUHAwEGCCsG AQUFBwMCMAwGA1UdEwEB/wQCMAAwHQYDVR0OBBYEFCYVR8obVWxbc3VF/PSEvna+ QMfGMB8GA1UdIwQYMBaAFKhKamMEfd265tE5t6ZFZe/zqOyhMG8GCCsGAQUFBwEB BGMwYTAuBggrBgEFBQcwAYYiaHR0cDovL29jc3AuaW50LXgzLmxldHNlbmNyeXB0 Lm9yZzAvBggrBgEFBQcwAoYjaHR0cDovL2NlcnQuaW50LXgzLmxldHNlbmNyeXB0 Lm9yZy8wUwYDVR0RBEwwSoIQbzJiaGVhbHRoeS5jby5ueoINbzJiaGVhbHRoeS5u eoIUd3d3Lm8yYmhlYWx0aHkuY28ubnqCEXd3dy5vMmJoZWFsdGh5Lm56MEwGA1Ud IARFMEMwCAYGZ4EMAQIBMDcGCysGAQQBgt8TAQEBMCgwJgYIKwYBBQUHAgEWGmh0 dHA6Ly9jcHMubGV0c2VuY3J5cHQub3JnMIIBAwYKKwYBBAHWeQIEAgSB9ASB8QDv AHYAsh4FzIuizYogTodm+Su5iiUgZ2va+nDnsklTLe+LkF4AAAFuqHJuagAABAMA RzBFAiAt4f+LlBlkRLgMY/8GWzTlrlex5poAfMNEb9qrhuT1DQIhAIg3lJUicpev hq29RdAcxg444QkiGLL1DzLtVBJSBb8zAHUAb1N2rDHwMRnYmQCkURX/dxUcEdkC wQApBo2yCJo32RMAAAFuqHJv2QAABAMARjBEAiAg/SlOEC5v/t4PZakjkUoBCXvA JmxXOjMF5ubATK0iVgIgBMQZLNqH1QeH8dox8bGw0po42vk0HYAIA27iwEgQvw0w DQYJKoZIhvcNAQELBQADggEBAGQO0XVB7YZIZvpWlfJ1qWRNNZ1MU8AV2WCfoDkS hPqeOL+gBLOx+6nFysQjJNvmUnR4hXpsh+iD9V0E9CVvaQAw+O6vsC7Rvw8xwN6a AfMQjvopcT8tH3jnzthIP3HFN6OV9PbkLTAKkFdHDzIDtjmaPSIfYMrhPcblyCGJ G86VT8Hwepx6/CSOoDMQinitxHXleNrKILDiMcGzQZ3hiRQkd1eEH8mvoMcmpQt1 jHha0hwVnQ0HgVXKbmZa2tnAnBVpJepc8oVKYaqWP7fPzGwMaX6H32a3HBQwy5+h OGpCZhIexNL5wAYRcqcqNsgr++04aJNzYn2aHXsgbXWAQ6Q= -----END CERTIFICATE-----
Public Key (PEM)
-----BEGIN PUBLIC KEY----- MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAwp1970hAlB/Xqb9ddqc6 y3eSsySUOI34g9IoKfRRWYl/34Or5n3rfzlso8ZaYL5ueodzpJl3ZWi1RZGmGdRF gNobIDZZatpVlTvXoIrLB4N0OuSkIPo4/Kl4QJPU/QuuRNKPhrab1bv1POjqIuyC qOu/gs9MsuwGDxkoDev4Qt7yd6XVUOxGN3gxeFQbIt86ReHyjNpYKXxMdXcC0zsK jJ+yUGHj9c0G63kf5spxLQYIYxXsqL8/Ss60P+Vj66RiskBruer0fWckL1TVJMbV Gk5Hn499MT+lUhZYlUrZCecY6zbFAeNL0uRJvBrQcLMdHOULCbHV9wZo8I/5eSuq ZwIDAQAB -----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 296888388642136256196673329971576543032710 . . . . . . . . [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 2019-11-26 15:01:41 +0000 UTC . . . . . . . . . . . . [c:0|t:23|false] UTCTime 2020-02-24 15:01:41 +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 'o2bhealthy.co.nz' . . . . . . . . [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 24567893329793921472219268774706596209162906573327252561918924482407948318974414754823482619352386406754576938439723931772820751037928480238077585531961885745656680577072932898854977905840000844014618971165327601955823420629529633187054749775579936857993164363955288821226759853410151482084852083486478918999053207762839104266169849902448418931529194581344355422330674058000370229582800037226332630391763619679039598171125704593817844383070981536821500135553680455552206643713834994305198665219025426981592051998308417818019347290009422967716531468288950608455618261251936735923056049064145278315480264816965125384807 . . . . . . . . . . . . . . . . . . . . [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) 261547ca1b556c5b737545fcf484be76be40c7c6 . . . . . . . . . . . . . . . . [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 (76 bytes) . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:2|false] IA5String 'o2bhealthy.co.nz' . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:2|false] IA5String 'o2bhealthy.nz' . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:2|false] IA5String 'www.o2bhealthy.co.nz' . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:2|false] IA5String 'www.o2bhealthy.nz' . . . . . . . . . . . . . . . . [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) 00ef007600b21e05cc8ba2cd8a204e8766f92bb98a2520676bdafa70e7b249532def8b905e0000016ea8726e6a000004030047304502202de1ff8b94196444b80c63ff065b34e5ae57b1e69a007cc3446fdaab86e4f50d02210088379495227297af86adbd45d01cc60e38e1092218b2f50f32ed54125205bf330075006f5376ac31f03119d89900a45115ff77151c11d902c10029068db2089a37d9130000016ea8726fd90000040300463044022020fd294e102e6ffede0f65a923914a01097bc0266c573a3305e6e6c04cad2256022004c4192cda87d50787f1da31f1b1b0d29a38daf9341d8008036ee2c04810bf0d . . . . [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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