www.worldnow.co.kr

Issued by EssentialSSL CA

About this certificate


This digital certificate with serial number b7:f7:34:54:1b:15:16:3e:a2:4d:c8:81:6f:32:91:bd was issued on by COMODO CA Limited .

With 2 subject alternative names this certificate can be used to secure multiple fqdn's. While the 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.

Cerificate errors/warnings *beta

  • ERROR: Certificate contains a key usage different from ServerAuth, ClientAuth or ServerGatedCrypto

www.worldnow.co.kr

Organization unit: Domain Control Validated
Organization unit: Hosted by Korea Information Certificate Authority, Inc.
Organization unit: EssentialSSL

COMODO CA Limited

Organization: COMODO CA Limited

Time since certificate expired

This certificate has expire since

Certificate Details

Serial Number (hex): b7:f7:34:54:1b:15:16:3e:a2:4d:c8:81:6f:32:91:bd
Serial Number (int): 244532281901544336005554331775396909501
Serial Number lenght: 128 bits, 16 octets

SubjectKeyId: 0a:01:f8:2a:ae:a1:b9:e2:cc:cb:b2:d9:e6:68:64:8a:6e:0b:b9:3b
AuthorityKeyId: da:cb:ea:ad:5b:08:5d:cc:ff:fc:26:54:ce:49:e5:55:c6:38:f4:f8

Fingerprint (sha1): cc:52:3f:33:9a:21:42:00:f9:78:b8:3b:eb:ec:2f:54:b1:36:33:75
Fingerprint (sha256): a3:54:e1:2e:fc:7d:58:05:47:cb:dd:7e:cb:bd:10:ee:f4:1c:be:75:cd:ec:53:5b:3f:cf:f9:c4:88:96:31:22

Issuing Certificate URL: http://crt.comodoca.com/EssentialSSLCA_2.crt

Revocation information

OCSP Server: http://ocsp.comodoca.com
CRL Distribution Point: http://crl.comodoca.com/EssentialSSLCA.crl

Check the revocation status for the current certificate on www.worldnow.co.kr
2
DNS Names
0
Email Addresses
0
IP Addresses

Advanced Certificate Properties

Technical details about this certificate


Public Key Algorithm

RSA

Key Size

2048

Signature Algorithm

SHA1 with RSA



Key Usage

Digital Signature
Key Encipherment

Extended Key Usages

Server Authentication
Client Authentication
Microsoft Server-Gated Cryptography
Netscape Server-Gated Cryptography

Extensions

9 extensions
No unhandled critical extensions



CA Certificate

This is not a CA certificate

Subject Alternative Names

www.worldnow.co.kr
worldnow.co.kr

Certificate

The complete raw certificate details in PEM and ASN.1 format.

Certificate (PEM)

-----BEGIN CERTIFICATE----- MIIFXjCCBEagAwIBAgIRALf3NFQbFRY+ok3IgW8ykb0wDQYJKoZIhvcNAQEFBQAw cjELMAkGA1UEBhMCR0IxGzAZBgNVBAgTEkdyZWF0ZXIgTWFuY2hlc3RlcjEQMA4G A1UEBxMHU2FsZm9yZDEaMBgGA1UEChMRQ09NT0RPIENBIExpbWl0ZWQxGDAWBgNV BAMTD0Vzc2VudGlhbFNTTCBDQTAeFw0xNDA4MTIwMDAwMDBaFw0xNTA4MTQyMzU5 NTlaMIGZMSEwHwYDVQQLExhEb21haW4gQ29udHJvbCBWYWxpZGF0ZWQxQDA+BgNV BAsTN0hvc3RlZCBieSBLb3JlYSBJbmZvcm1hdGlvbiBDZXJ0aWZpY2F0ZSBBdXRo b3JpdHksIEluYy4xFTATBgNVBAsTDEVzc2VudGlhbFNTTDEbMBkGA1UEAxMSd3d3 Lndvcmxkbm93LmNvLmtyMIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA rkBVKVuQbBeUHvQpRfilJDorqypQbj7sZrb4BeDp1i5CWnvSTGAnWDdX0NzMUqK/ SSY9UnCMv7n9D3q9yG6yoVGTBhYC8jEAV2i/tRN0b+n74TYl08Q6khKkTOja3ikf n4PTdCLSw/ipea1MwTMuyXSneNa9dKleEzzL01oIfbgFQYwswJcRVzl/7dduHDX7 obLtnj3MHGHuekWVajPNgCBVYsJ7PNovg0151z782+k9cP7HqzjRRB3OjQkHgtm1 fqW/M4PtTbN8DV865wetA9X3F1I/PT26pP7QWtgQzk1n+AXOB5FlGg58TXe5q+6H XnBzZqZhp2rRZXESr0MofwIDAQABo4IBxTCCAcEwHwYDVR0jBBgwFoAU2svqrVsI Xcz//CZUzknlVcY49PgwHQYDVR0OBBYEFAoB+CquobnizMuy2eZoZIpuC7k7MA4G A1UdDwEB/wQEAwIFoDAMBgNVHRMBAf8EAjAAMDQGA1UdJQQtMCsGCCsGAQUFBwMB BggrBgEFBQcDAgYKKwYBBAGCNwoDAwYJYIZIAYb4QgQBME8GA1UdIARIMEYwOgYL KwYBBAGyMQECAgcwKzApBggrBgEFBQcCARYdaHR0cHM6Ly9zZWN1cmUuY29tb2Rv LmNvbS9DUFMwCAYGZ4EMAQIBMDsGA1UdHwQ0MDIwMKAuoCyGKmh0dHA6Ly9jcmwu Y29tb2RvY2EuY29tL0Vzc2VudGlhbFNTTENBLmNybDBuBggrBgEFBQcBAQRiMGAw OAYIKwYBBQUHMAKGLGh0dHA6Ly9jcnQuY29tb2RvY2EuY29tL0Vzc2VudGlhbFNT TENBXzIuY3J0MCQGCCsGAQUFBzABhhhodHRwOi8vb2NzcC5jb21vZG9jYS5jb20w LQYDVR0RBCYwJIISd3d3Lndvcmxkbm93LmNvLmtygg53b3JsZG5vdy5jby5rcjAN BgkqhkiG9w0BAQUFAAOCAQEAi2nK1DeV4eW/Uq4LHFb/i0nqLB/qLcCm+cEqYtqM xSmhX/gvyVxcjSvZte6tc3Wq/J/7MDWr6hptfeOb1IuB4+dAa8ZuMgNFCSdkCtiy yyUtY9faTHZpaTsA5/vz7c+Mdp1QKrEYRbnypR5QldO9axTGP/Oo69DBJ3dJAKTq xIO3nUWtdySvm7mod0nu9obgV5RW4OMe3iw35BwSYmYoHnjrdKqkIj/jSZNmSifV g4X3QNTUHB7EVCCr30oP81GufTqGd00H2iv4Vp5CnywdANmtSCMUb2gn/SO/UoGf XqRjtxREg+hSQ75s4C3Qvt/Dhnzd6PSvJFYt1CzuLHVrCg== -----END CERTIFICATE-----

Public Key (PEM)

-----BEGIN PUBLIC KEY----- MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEArkBVKVuQbBeUHvQpRfil JDorqypQbj7sZrb4BeDp1i5CWnvSTGAnWDdX0NzMUqK/SSY9UnCMv7n9D3q9yG6y oVGTBhYC8jEAV2i/tRN0b+n74TYl08Q6khKkTOja3ikfn4PTdCLSw/ipea1MwTMu yXSneNa9dKleEzzL01oIfbgFQYwswJcRVzl/7dduHDX7obLtnj3MHGHuekWVajPN gCBVYsJ7PNovg0151z782+k9cP7HqzjRRB3OjQkHgtm1fqW/M4PtTbN8DV865wet A9X3F1I/PT26pP7QWtgQzk1n+AXOB5FlGg58TXe5q+6HXnBzZqZhp2rRZXESr0Mo fwIDAQAB -----END PUBLIC KEY-----

ASN1 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 244532281901544336005554331775396909501 . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 1.2.840.113549.1.1.5 (sha1WithRSAEncryption) . . . . . . . . . . . . [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 'GB' . . . . . . . . . . . . [c:0|t:17|true] SET, SET OF . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 2.5.4.8 (stateOrProvinceName) . . . . . . . . . . . . . . . . . . . . [c:0|t:19|false] PrintableString 'Greater Manchester' . . . . . . . . . . . . [c:0|t:17|true] SET, SET OF . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 2.5.4.7 (localityName) . . . . . . . . . . . . . . . . . . . . [c:0|t:19|false] PrintableString 'Salford' . . . . . . . . . . . . [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 'COMODO CA Limited' . . . . . . . . . . . . [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 'EssentialSSL CA' . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF . . . . . . . . . . . . [c:0|t:23|false] UTCTime 2014-08-12 00:00:00 +0000 UTC . . . . . . . . . . . . [c:0|t:23|false] UTCTime 2015-08-14 23:59:59 +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 2.5.4.11 (organizationalUnitName) . . . . . . . . . . . . . . . . . . . . [c:0|t:19|false] PrintableString 'Domain Control Validated' . . . . . . . . . . . . [c:0|t:17|true] SET, SET OF . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 2.5.4.11 (organizationalUnitName) . . . . . . . . . . . . . . . . . . . . [c:0|t:19|false] PrintableString 'Hosted by Korea Information Certificate Authority, Inc.' . . . . . . . . . . . . [c:0|t:17|true] SET, SET OF . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 2.5.4.11 (organizationalUnitName) . . . . . . . . . . . . . . . . . . . . [c:0|t:19|false] PrintableString 'EssentialSSL' . . . . . . . . . . . . [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 'www.worldnow.co.kr' . . . . . . . . [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 21997188682238646258542214250986640793142813957999143630978643225420235471968584894200717912098742284283439846193321660289239332641368135384883816563124161613395929102656530978589747102704764576722250708542255202331882951631444721436730330469005372555002249832482051557433771149969144820258257167179186675470774708422525614784854224160220555412616690618728968431149830139545183739199808034087872119740915408815174530762440749601136665716567135221342686440077611447630335341465496472643935482696660139308607466852943259346789669444278916974672644551641869032306812751642643441162447635530206325376412679572865687955583 . . . . . . . . . . . . . . . . . . . . [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 2.5.29.35 (authorityKeyIdentifier) . . . . . . . . . . . . . . . . . . . . [c:0|t:4|false] OCTET STRING (24 bytes) . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:0|false] OtherName dacbeaad5b085dccfffc2654ce49e555c638f4f8 . . . . . . . . . . . . . . . . [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) 0a01f82aaea1b9e2cccbb2d9e668648a6e0bb93b . . . . . . . . . . . . . . . . [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 2.5.29.19 (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 2.5.29.37 (extKeyUsage) . . . . . . . . . . . . . . . . . . . . [c:0|t:4|false] OCTET STRING (45 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:6|false] OBJECT IDENTIFIER 1.3.6.1.4.1.311.10.3.3 (serverGatedCrypto) . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 2.16.840.1.113730.4.1 (serverGatedCrypto) . . . . . . . . . . . . . . . . [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 (72 bytes) . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 1.3.6.1.4.1.6449.1.2.2.7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [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 'https://secure.comodo.com/CPS' . . . . . . . . . . . . . . . . . . . . . . . . . . . . [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 2.5.29.31 (cRLDistributionPoints) . . . . . . . . . . . . . . . . . . . . [c:0|t:4|false] OCTET STRING (52 bytes) . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:0|true] OtherName . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:0|true] OtherName . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:6|false] IA5String 'http://crl.comodoca.com/EssentialSSLCA.crl' . . . . . . . . . . . . . . . . [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 (98 bytes) . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 1.3.6.1.5.5.7.48.2 (caIssuers) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:6|false] IA5String 'http://crt.comodoca.com/EssentialSSLCA_2.crt' . . . . . . . . . . . . . . . . . . . . . . . . . . . . [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.comodoca.com' . . . . . . . . . . . . . . . . [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 (38 bytes) . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:2|false] IA5String 'www.worldnow.co.kr' . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:2|false] IA5String 'worldnow.co.kr' . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF . . . . . . . . [c:0|t:6|false] OBJECT IDENTIFIER 1.2.840.113549.1.1.5 (sha1WithRSAEncryption) . . . . . . . . [c:0|t:5|false] NULL . . . . [c:0|t:3|false] BIT STRING (2048 bits) 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