cms.3xw.de

Issued by Let's Encrypt Authority X3

About this certificate

This digital certificate with serial number 03:2f:43:37:60:f6:8f:59:51:9a:2b:f6:28:87:68:00:e2:b4 was issued on by Let's Encrypt.

With 3 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=cms.3xw.de

Let's Encrypt

Organization: Let's Encrypt
Country: US

This certificate has expire since

Certificate Details

Serial Number (hex): 03:2f:43:37:60:f6:8f:59:51:9a:2b:f6:28:87:68:00:e2:b4
Serial Number (int): 277419474859255470766881866564742575874740
Serial Number lenght: 138 bits, 18 octets

SubjectKeyId: 09:a4:9c:d9:e6:d8:33:d7:12:d7:e2:f8:ce:99:91:4d:3e:9b:f9:a1
AuthorityKeyId: a8:4a:6a:63:04:7d:dd:ba:e6:d1:39:b7:a6:45:65:ef:f3:a8:ec:a1

Fingerprint (sha1): da:3b:ef:a0:ce:2c:df:5f:7f:69:68:ba:07:86:8c:c4:d9:64:78:79
Fingerprint (sha256): a0:00:03:b1:2f:06:41:89:36:8e:44:d8:98:d3:0e:b0:95:c0:c3:67:67:50:8b:02:28:c4:c8:d4:c2:67:8d:9c

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 cms.3xw.de

3

DNS Names

0

Email Addresses

0

IP Addresses

Advanced Certificate Properties

Tehnical certificate details for cms.3xw.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

cms.3xw.de
patzelt.de
vincp3.de

Other certificates including the domain name 3xw.de

(limited to 100 certificates)
cms.3xw.de
cms.3xw.de
cms.3xw.de
cms.3xw.de
cms.3xw.de
cms.3xw.de
3xw.de
cms.3xw.de
cms.3xw.de
cms.3xw.de
cms.3xw.de
cms.3xw.de
cms.3xw.de
cms.3xw.de
cms.3xw.de
cms.3xw.de
cms.3xw.de
cms.3xw.de
cms.3xw.de
cms.3xw.de
cms.3xw.de

Certificate

The complete raw certificate details for cms.3xw.de in PEM and ASN.1 format.

Certificate (PEM)

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

Public Key (PEM)

-----BEGIN PUBLIC KEY-----
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA4KzoZUB1B34dshrp4ITV
XlSYuqrSoF95Ck+5qzanJEys8/Bb/40RsH/LjEukfusX6wxUvvHUXQ28k2WVod5A
D/L2IGEBp1VnnnfFMSc3u3wOgYuAH8ZWjC/fxNn7s+beVoHennYG5TSTXHCTzAkO
CtOAlFDybSGNURaPZnYtgZ1noAsJyMIn5e1CA9OT+JhFLKNo06hSA8cep+yrz3UG
6kCml52EKpB5v2H6JWkajscUU8UflXzuELbXzSlthluxCSLIdw6yzGAreqlHRifw
SDL4vpK9HbLGbXGj/EslrxN4pOXXzJ2kIkWhAZYwCuBAa1z/itjniKJN4+o6/vsI
qwIDAQAB
-----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 277419474859255470766881866564742575874740
 . . . . . . . . [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 2018-10-07 05:04:09 +0000 UTC
 . . . . . . . . . . . . [c:0|t:23|false] UTCTime 2019-01-05 05:04:09 +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 'cms.3xw.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 28362644323934821260342001046910055569695432250086638804721257024519950999627711301612880845095112246697962238640399685100201945107173918259100740658058014069369419261825995202308668032080929347957608223768528744114134578927327990846621204178370496753933178355176287116759450889150866141071893926429592277835424127849807261761849835236655584271873563575682351963540161168720624682261044792947368255374439073742731052100227779537212312068636826953390357126391906621921922697093414082864979749168052607637606934492042904668445930041655940768100966739901134407277210429386489802292360271484395445950883466503295893964971
 . . . . . . . . . . . . . . . . . . . . [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)
							09a49cd9e6d833d712d7e2f8ce99914d3e9bf9a1
 . . . . . . . . . . . . . . . . [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 (37 bytes)
 . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:2|false] IA5String 'cms.3xw.de'
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:2|false] IA5String 'patzelt.de'
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:2|false] IA5String 'vincp3.de'
 . . . . . . . . . . . . . . . . [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 (246 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 1.3.6.1.5.5.7.2.2 (unotice)
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:12|false] UTF8String 'This Certificate may only be relied upon by Relying Parties and only in accordance with the Certificate Policy found at https://letsencrypt.org/repository/'
 . . . . . . . . . . . . . . . . [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 (245 bytes)
 . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:4|false] OCTET STRING (242 bytes)
							00f0007600e2694bae26e8e94009e8861bb63b83d43ee7fe7488fba48f2893019dddf1dbfe000001664d20399f000004030047304502202d490a16050f5ec75e30f407bb3236c01467e457772df6d49183fecc3febee3c0221008d23f511140c229d8eba8d46158f3c7dfe9f01216bd6002b4619f2ba5b2719f7007600293c519654c83965baaa50fc5807d4b76fbf587a2972dca4c30cf4e54547f478000001664d203ba50000040300473045022100cc26d776b52ebcb0783c14322b2540aca654298d4910a58588e04bd0da2ae2cb022066a4eb9b47933103567ab0e89546d7a45f975f9dd05068880525fda3fc94180d
 . . . . [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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