www.buzztouch.de

Issued by COMODO RSA Domain Validation Secure Server CA

About this certificate

This digital certificate with serial number 8f:c5:bc:63:01:8c:12:71:55:7b:57:2b:18:f5:49:24 was issued on by COMODO CA Limited.

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=www.buzztouch.de,OU=Domain Control Validated+OU=PositiveSSL

COMODO CA Limited

Organization: COMODO CA Limited
State / Province: Greater Manchester
Locality: Salford
Country: GB

This certificate has expire since

Certificate Details

Serial Number (hex): 8f:c5:bc:63:01:8c:12:71:55:7b:57:2b:18:f5:49:24
Serial Number (int): 191106306815446728012079819134988536100
Serial Number lenght: 128 bits, 16 octets

SubjectKeyId: b4:90:5c:cd:6f:ed:71:37:df:d0:b3:d3:c7:c4:06:95:2c:07:c8:6f
AuthorityKeyId: 90:af:6a:3a:94:5a:0b:d8:90:ea:12:56:73:df:43:b4:3a:28:da:e7

Fingerprint (sha1): b7:db:9a:73:3f:1a:c7:e9:0c:c4:f2:88:02:4f:72:31:0c:5f:67:f6
Fingerprint (sha256): f3:55:d1:89:99:c4:85:ec:ce:3a:db:b4:d8:b6:18:7a:c3:24:e3:94:f5:5a:6e:73:6e:fc:40:92:69:eb:4f:a5

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

Revocation information

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

Check the revocation status for certificate www.buzztouch.de

2

DNS Names

0

Email Addresses

0

IP Addresses

Advanced Certificate Properties

Tehnical certificate details for www.buzztouch.de

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

www.buzztouch.de
buzztouch.de

Other certificates including the domain name buzztouch.de

(limited to 100 certificates)

Certificate

The complete raw certificate details for www.buzztouch.de in PEM and ASN.1 format.

Certificate (PEM)

-----BEGIN CERTIFICATE-----
MIIFTTCCBDWgAwIBAgIRAI/FvGMBjBJxVXtXKxj1SSQwDQYJKoZIhvcNAQELBQAw
gZAxCzAJBgNVBAYTAkdCMRswGQYDVQQIExJHcmVhdGVyIE1hbmNoZXN0ZXIxEDAO
BgNVBAcTB1NhbGZvcmQxGjAYBgNVBAoTEUNPTU9ETyBDQSBMaW1pdGVkMTYwNAYD
VQQDEy1DT01PRE8gUlNBIERvbWFpbiBWYWxpZGF0aW9uIFNlY3VyZSBTZXJ2ZXIg
Q0EwHhcNMTYwOTI5MDAwMDAwWhcNMTgwOTI5MjM1OTU5WjBUMSEwHwYDVQQLExhE
b21haW4gQ29udHJvbCBWYWxpZGF0ZWQxFDASBgNVBAsTC1Bvc2l0aXZlU1NMMRkw
FwYDVQQDExB3d3cuYnV6enRvdWNoLmRlMIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8A
MIIBCgKCAQEAxVcyWKjpnC5Dk16yVJ8TgZmq6u5iJFKTifpWQaae23gmcJaAXAzS
Bxs1kZgCKdQ+RQikwUb/ac5oZox5B0+payCTl2ROWx/tnDvXisaCuHR2eGZvLgaF
BB/wflEykYf7FsqVf5JD1IBpEIMNUgvhi5o6drb/Igo8UgycEC2X6c99ntgkYT2Z
KoqePeEUF7kyN9VcK8ncDjKTXkjSuPtdfmUMMCCbr8WcUO4f9e0ZVNuw1LqvWwUa
KuqxJxARMfwogAgc3hnLsFyBOfFwjJ7yXDQSPK1KR43eOeMK2wO83obd7SNFohio
CT08S6soCgMXeLUdKGWFqyMGTp8lYcnVwQIDAQABo4IB2zCCAdcwHwYDVR0jBBgw
FoAUkK9qOpRaC9iQ6hJWc99DtDoo2ucwHQYDVR0OBBYEFLSQXM1v7XE339Cz08fE
BpUsB8hvMA4GA1UdDwEB/wQEAwIFoDAMBgNVHRMBAf8EAjAAMB0GA1UdJQQWMBQG
CCsGAQUFBwMBBggrBgEFBQcDAjBPBgNVHSAESDBGMDoGCysGAQQBsjEBAgIHMCsw
KQYIKwYBBQUHAgEWHWh0dHBzOi8vc2VjdXJlLmNvbW9kby5jb20vQ1BTMAgGBmeB
DAECATBUBgNVHR8ETTBLMEmgR6BFhkNodHRwOi8vY3JsLmNvbW9kb2NhLmNvbS9D
T01PRE9SU0FEb21haW5WYWxpZGF0aW9uU2VjdXJlU2VydmVyQ0EuY3JsMIGFBggr
BgEFBQcBAQR5MHcwTwYIKwYBBQUHMAKGQ2h0dHA6Ly9jcnQuY29tb2RvY2EuY29t
L0NPTU9ET1JTQURvbWFpblZhbGlkYXRpb25TZWN1cmVTZXJ2ZXJDQS5jcnQwJAYI
KwYBBQUHMAGGGGh0dHA6Ly9vY3NwLmNvbW9kb2NhLmNvbTApBgNVHREEIjAgghB3
d3cuYnV6enRvdWNoLmRlggxidXp6dG91Y2guZGUwDQYJKoZIhvcNAQELBQADggEB
AAviDbY35zM5KSL2bTod4jeaqVtgbTC5cIaFIjfS2zdb/h/3FThNviYEls4qnOUC
tHneS285Mss4Pf9Q8dDbMnKBU3BEi4r9ASUidj7EXSe8q+v2E9M/Ig1tnCD86Clu
QTDoByXlAwdwKtjhGSvvUiXHML7LXe/+bFNmKX1IdK3WJHz4A14K3NoFBgcotf98
JI05pmGnVCGVdCtO14sPpQse2ye+b2kB42slMQChQuZi+X2mI/V0/HlVcgXrw5uM
4g8ytjd+vA1sVHPo2Y+P55IVYGTk8ruKLbhyb/bjQ1eaSOdNZZGglUw2uP3aFpaa
s0aJoodqzEfxO8f4z+xzzcQ=
-----END CERTIFICATE-----

Public Key (PEM)

-----BEGIN PUBLIC KEY-----
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAxVcyWKjpnC5Dk16yVJ8T
gZmq6u5iJFKTifpWQaae23gmcJaAXAzSBxs1kZgCKdQ+RQikwUb/ac5oZox5B0+p
ayCTl2ROWx/tnDvXisaCuHR2eGZvLgaFBB/wflEykYf7FsqVf5JD1IBpEIMNUgvh
i5o6drb/Igo8UgycEC2X6c99ntgkYT2ZKoqePeEUF7kyN9VcK8ncDjKTXkjSuPtd
fmUMMCCbr8WcUO4f9e0ZVNuw1LqvWwUaKuqxJxARMfwogAgc3hnLsFyBOfFwjJ7y
XDQSPK1KR43eOeMK2wO83obd7SNFohioCT08S6soCgMXeLUdKGWFqyMGTp8lYcnV
wQIDAQAB
-----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 191106306815446728012079819134988536100
 . . . . . . . . [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 '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 'COMODO RSA Domain Validation Secure Server CA'
 . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . [c:0|t:23|false] UTCTime 2016-09-29 00:00:00 +0000 UTC
 . . . . . . . . . . . . [c:0|t:23|false] UTCTime 2018-09-29 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 'PositiveSSL'
 . . . . . . . . . . . . [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.buzztouch.de'
 . . . . . . . . [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 24911944356561174348569810089077555061817151472070044584420923965217294855382644014472263186014423136894055745543322501743189815069002769675716628372989261300453965212626259220509036703010694961435471764089056798168466729508426695197065323812744373649292043821833258364728490100525819711064244847739247234563850595229397073128404107222801799172418079670330813563362151386326260328849583703852372682250795573680517405826174369501614918478201217647071386686546328905136215966144142154417146564758935179208622004825180198987193424314536194227315724718304427477421668016033248313255842769916763190687052923804631595341249
 . . . . . . . . . . . . . . . . . . . . [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 90af6a3a945a0bd890ea125673df43b43a28dae7
 . . . . . . . . . . . . . . . . [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)
							b4905ccd6fed7137dfd0b3d3c7c406952c07c86f
 . . . . . . . . . . . . . . . . [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 (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 2.5.29.32 (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 (77 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/COMODORSADomainValidationSecureServerCA.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 (121 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/COMODORSADomainValidationSecureServerCA.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 (34 bytes)
 . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:2|false] IA5String 'www.buzztouch.de'
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:2|false] IA5String 'buzztouch.de'
 . . . . [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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