serasera.org

Issued by Let's Encrypt Authority X3

About this certificate

This digital certificate with serial number 03:27:33:5c:03:26:cf:58:ba:e5:04:74:b5:be:7a:68:c3:f2 was issued on by Let's Encrypt.

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=serasera.org

Let's Encrypt

Organization: Let's Encrypt
Country: US

This certificate has expire since

Certificate Details

Serial Number (hex): 03:27:33:5c:03:26:cf:58:ba:e5:04:74:b5:be:7a:68:c3:f2
Serial Number (int): 274676138488215425580190219068100009575410
Serial Number lenght: 138 bits, 18 octets

SubjectKeyId: a1:f9:ca:a7:44:70:84:8e:0a:56:c4:29:72:7e:e6:97:cc:af:06:80
AuthorityKeyId: a8:4a:6a:63:04:7d:dd:ba:e6:d1:39:b7:a6:45:65:ef:f3:a8:ec:a1

Fingerprint (sha1): 16:7e:8d:3f:d8:2f:58:f7:8d:f1:fa:1e:c7:a8:63:ee:7d:c9:63:b2
Fingerprint (sha256): 88:e4:e0:0d:ad:5d:46:fa:eb:8b:7c:ee:35:f4:a8:a0:1f:0c:ec:e8:cf:68:2b:c3:55:2b:2b:cf:8e:48:2d:31

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 serasera.org

2

DNS Names

0

Email Addresses

0

IP Addresses

Advanced Certificate Properties

Tehnical certificate details for serasera.org

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

serasera.org
www.serasera.org

Other certificates including the domain name serasera.org

(limited to 100 certificates)
reinofloral.adparis.es
avatar.serasera.org
ohabolana.org
dev.vitau.el-pixel.com
hml.premiando.app
serasera.org
tononkira.serasera.org
ec.ar-ap-inc.jp
namana.serasera.org
botogasy.serasera.org
www.fetanx.com
namana.serasera.org
betterbriefs.dev
stephen.mooir.im
3m-staging-ideacloud.forgedx.com
tononkira.serasera.org
www.nyiritomas.com
arkx-store.com
kiteny.serasera.org
takila.serasera.org
ohabolana.org
avatar.serasera.org
login.serasera.org
ohabolana.org
botogasy.serasera.org
serasera.org
serasera.org
login.serasera.org
botogasy.serasera.org
hery.serasera.org
botogasy.serasera.org
storyflo.app
aveila.com
namana.serasera.org
invitr.in
tononkira.serasera.org
login.serasera.org
botogasy.serasera.org
takila.serasera.org
www.gofoods.pk
avatar.serasera.org
serasera.org
video.serasera.org
serasera.org
serasera.org
klipgasy.org
adonisvero.fr
adonisvero.fr
www.inov8tn.com
adonisvero.fr
login.serasera.org
avatar.serasera.org
germinate.world
vetso.serasera.org
botogasy.serasera.org
takila.serasera.org
aveila.com
serasera.org
www.blacklinecreative.com
takila.serasera.org
login.serasera.org
catastro.fiatauto.com.ar
ohabolana.org
www.gofoods.pk
login.serasera.org
tononkira.serasera.org
login.serasera.org
ohabolana.org
takila.serasera.org
botogasy.serasera.org
aamada.katolika.org
botogasy.serasera.org
avatar.serasera.org
1571leisureworld.com
namana.serasera.org
serasera.org
serasera.org
serasera.org
adonisvero.fr
tononkira.serasera.org
moontracer.xyz
avatar.serasera.org
serasera.org
www.proorganizer.com.ec
login.serasera.org
serasera.org
vetso.serasera.org
betterbriefs.dev
tononkira.serasera.org
login.serasera.org
www.rfsrentals.com
adonisvero.fr
login.serasera.org

Certificate

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

Certificate (PEM)

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

Public Key (PEM)

-----BEGIN PUBLIC KEY-----
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAvZSqXHKjvslFZKGEyKd5
7j27aU9AvQm2d8zfVO+PvaO1xN4B3mYo37FpnuOJAKeg4hkJC9hlmeXRH30o5UH7
WBTDGKZXMp7zVJOThR43MLdy4/64Hculymjn2FE8Un3v+vPSR/i9RZoJlGceCICg
Gi7g8+qJ0k0mewRemdSWQ4rW2jA3y65jAu0Fqk2d12lO6Suj25A42xcG6OVudaM7
sOqLjFXSmyRsoCMnaVidvK5U8ouRCzshGNVS4WZ4x2O76Ne4DX7iCYxY86Ali4Vy
pJzQ0OFJKv5jKkpWUuPM6b13yP9rsjlG8UoIvmWF8F9WaZ97v9VwQVdFfr51ah5c
UQIDAQAB
-----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 274676138488215425580190219068100009575410
 . . . . . . . . [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 2019-12-26 22:12:07 +0000 UTC
 . . . . . . . . . . . . [c:0|t:23|false] UTCTime 2020-03-25 22:12:07 +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 'serasera.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 (2160 bits)
 . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . [c:0|t:2|false] INTEGER 23932349315680309213030976936243298856957239039687532071160834231794045372814601130645723591570888951665595991277008781809042734844017290668999217858867242405037503413620013016911711005028655904568500497459863142345255290368389711083886398694287713329627264667119401175684435792793612912704060666071638849173760824670259451447663823271268536514301492197827082699207407333043193325519441896842856014583864017984098403922999128989853777956335451286390670902030383444399389213182570377497910881000203401252930423812741592887424592234301666093467546120774647130954274153901331423268875305352288379982383109700086082198609
 . . . . . . . . . . . . . . . . . . . . [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)
							a1f9caa74470848e0a56c429727ee697ccaf0680
 . . . . . . . . . . . . . . . . [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 (34 bytes)
 . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:2|false] IA5String 'serasera.org'
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:2|false] IA5String 'www.serasera.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 (246 bytes)
 . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:4|false] OCTET STRING (243 bytes)
							00f1007700b21e05cc8ba2cd8a204e8766f92bb98a2520676bdafa70e7b249532def8b905e0000016f447b45c30000040300483046022100c96ff696d3e0fef7d49e2e85da4d52431f0aa06e746f25b8c7913d2fb6b34a29022100a7b1e3f56878a6e15f5f243ee79a3c162852bb9fc716a2ef612965b8c3dfdb1a0076006f5376ac31f03119d89900a45115ff77151c11d902c10029068db2089a37d9130000016f447b47100000040300473045022100fab65ffc1af782c4e54be9577bac759eff248b7edac6432d2246f36a7b54c57b02200ad2a33fdf23aa85a25632d48ca2ad16184180241e41f8757d64654b7ff80344
 . . . . [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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