www.romanodilombardia.org

Issued by Let's Encrypt Authority X3

About this certificate

This digital certificate with serial number 03:59:46:ba:1f:93:c9:72:1f:05:13:59:8b:c8:03:77:11:46 was issued on by Let's Encrypt.

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.romanodilombardia.org

Let's Encrypt

Organization: Let's Encrypt
Country: US

This certificate has expire since

Certificate Details

Serial Number (hex): 03:59:46:ba:1f:93:c9:72:1f:05:13:59:8b:c8:03:77:11:46
Serial Number (int): 291716000818628476830957367919295929454918
Serial Number lenght: 138 bits, 18 octets

SubjectKeyId: 03:5b:21:cc:f2:9b:5a:83:20:f8:8d:43:00:36:31:32:5a:d3:ab:a8
AuthorityKeyId: a8:4a:6a:63:04:7d:dd:ba:e6:d1:39:b7:a6:45:65:ef:f3:a8:ec:a1

Fingerprint (sha1): 3a:d1:a7:e5:a2:26:cd:3c:2d:1b:d5:ce:43:88:59:8e:b2:25:07:fe
Fingerprint (sha256): c2:8e:a0:1d:14:e3:f5:90:d7:df:1f:15:0a:37:7b:d3:1d:cc:e0:97:7d:51:49:9c:f0:e2:e1:e3:47:75:1f:a9

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 www.romanodilombardia.org

1

DNS Names

0

Email Addresses

0

IP Addresses

Advanced Certificate Properties

Tehnical certificate details for www.romanodilombardia.org

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

www.romanodilombardia.org

Other certificates including the domain name romanodilombardia.org

(limited to 100 certificates)

Certificate

The complete raw certificate details for www.romanodilombardia.org 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 291716000818628476830957367919295929454918
 . . . . . . . . [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 2019-07-28 23:24:00 +0000 UTC
 . . . . . . . . . . . . [c:0|t:23|false] UTCTime 2019-10-26 23:24:00 +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 'www.romanodilombardia.org'
 . . . . . . . . [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 877640560096602826863413262655888139230108348831271682585472666782692211939540467656743529871080253817310580644716413914997525662681328269285078505508588638479912230282746037504139950955615355215931139990685148654085647533386422075492499904722061410254529078309736863456989107419370753231765400447546866545369462511883479682947173159302943232311831165120943655895837147313773519162734195930455741087462033917160469683738418132032606977496201071612151848871136645447890583511683998295150707995682907748358368247922765436305277725261081022407932558112295855104327537218232714340436989443547611986597150481317627201618596237860187814666655420419624015141940595618801045091689931362822440676576913520986502100432018723687728417559443263643721703287984985318841499219194246789557080293611786940524525993250094061797817760524142633315471508006937657526348476434773290817718482600038437526202183332301160153891998714357529930245212111088074026228434781170524055885174379751392127107088735350024992989158974753658832540235907144636196822710570059562183649260250708523668177981200846603619432982634733482817184306110140648672793128315336946686450621461427945516464763211009743396449800953354555422413245074876609345504990602498626784780216837
 . . . . . . . . . . . . . . . . . . . . [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)
							035b21ccf29b5a8320f88d43003631325ad3aba8
 . . . . . . . . . . . . . . . . [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 (29 bytes)
 . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:2|false] IA5String 'www.romanodilombardia.org'
 . . . . . . . . . . . . . . . . [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)
							00ef007500e2694bae26e8e94009e8861bb63b83d43ee7fe7488fba48f2893019dddf1dbfe0000016c3b1cd604000004030046304402202b8e23fd961fc4809e53c3f2e90bca261f547246eee69220f6b5c931fb7606ae0220064d1b6aaa1045a0abcc0340bfbfc040107a55f0a56b1ab153dcdf317ef01189007600293c519654c83965baaa50fc5807d4b76fbf587a2972dca4c30cf4e54547f4780000016c3b1cd4050000040300473045022052b53966690d44fd2a1733ca26aa65aac3314bfd142824a7cedf7f2f3c50b4da022100ff57eaf7e774e7ed3472312845dd6627463444376f867d2d37f96b1c4bd4d20b
 . . . . [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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