www.airforce-cases.com

Issued by Let's Encrypt Authority X3

About this certificate

This digital certificate with serial number 03:2d:bb:d2:f5:27:01:1e:53:65:97:a6:a3:08:28:f1:73:55 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.airforce-cases.com

Let's Encrypt

Organization: Let's Encrypt
Country: US

This certificate has expire since

Certificate Details

Serial Number (hex): 03:2d:bb:d2:f5:27:01:1e:53:65:97:a6:a3:08:28:f1:73:55
Serial Number (int): 276899225296555639757088998814124382188373
Serial Number lenght: 138 bits, 18 octets

SubjectKeyId: 62:49:4f:73:ec:79:6f:63:d5:c0:dd:3e:75:05:20:10:c8:d0:70:38
AuthorityKeyId: a8:4a:6a:63:04:7d:dd:ba:e6:d1:39:b7:a6:45:65:ef:f3:a8:ec:a1

Fingerprint (sha1): 11:40:0f:3d:2d:95:46:30:10:cb:b2:f9:89:06:89:42:28:e9:60:86
Fingerprint (sha256): fb:6f:5a:eb:a3:f8:c3:42:6b:ca:ba:bc:41:e1:bb:6f:6e:78:2b:65:8b:4b:ec:4b:5f:ca:37:44:50:d2:b2:1c

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.airforce-cases.com

1

DNS Names

0

Email Addresses

0

IP Addresses

Advanced Certificate Properties

Tehnical certificate details for www.airforce-cases.com

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.airforce-cases.com

Other certificates including the domain name airforce-cases.com

(limited to 100 certificates)

Certificate

The complete raw certificate details for www.airforce-cases.com in PEM and ASN.1 format.

Certificate (PEM)

-----BEGIN CERTIFICATE-----
MIIGZTCCBU2gAwIBAgISAy270vUnAR5TZZemowgo8XNVMA0GCSqGSIb3DQEBCwUA
MEoxCzAJBgNVBAYTAlVTMRYwFAYDVQQKEw1MZXQncyBFbmNyeXB0MSMwIQYDVQQD
ExpMZXQncyBFbmNyeXB0IEF1dGhvcml0eSBYMzAeFw0xOTEyMDUwODI5MDhaFw0y
MDAzMDQwODI5MDhaMCExHzAdBgNVBAMTFnd3dy5haXJmb3JjZS1jYXNlcy5jb20w
ggIiMA0GCSqGSIb3DQEBAQUAA4ICDwAwggIKAoICAQDjNomryFpjC0BFaOS0+d28
dh+O3zkhIhgbVgMli/TTiBxiCda6FfHu8T0Fplf3KA4uApU4UiktP1DsKrpa0fmR
CELc/zTCQ8DKHeCYTJDyyS22UmN1agUYyL7Z7Y9BQC1UfGPM6JqafF28BMGkv5ip
22XJw6tElVeYcTVhXJ1gmDKz9iy0VHHODo+JoSrZbXX/Qx8gKBIbKn6Y5szKr4/B
vrpjoVD72YwIzwGyCUcf5lBX9invTcaOJw/2paqaZves+3uI9dCcGJFCgas0rMV9
hypejPFX+zPQu4UM2FGtNfyVLgQZN5tT9fDE+AszGJIwGa16cyOMBp2Ic2uC/q1Q
X+7AMb26Kq/VkIsTCJlhURyd/49v7PJaEWtQqXoiSwMGVItDcuhIVD9LZYOba039
p/Xsav11IBx667GsRr2m1MZZ2nJTFFTBu9gXz+8ngRDXZeZtt9p4WbguBDRhMXLN
IzdfkIeZ28iU3JkEhKhvbB3bNE9T/sUX6vrZVQyVhcnj2fNQ4DGTeZEyQgePxm1M
jN+IdX64ZCltxOb6M68R1Y88Sr7vmNOZ8lkAn28YzjBLqxk7N8kmLYPVVGy7wtdC
FIKSgzE/xETN2WlrUy0/xkSF4OxixlX5J8dFRTdKUScqx3qSgWu39o0D0bKSlEwJ
HQKZWPBmOMDqOTTiVF25IQIDAQABo4ICbDCCAmgwDgYDVR0PAQH/BAQDAgWgMB0G
A1UdJQQWMBQGCCsGAQUFBwMBBggrBgEFBQcDAjAMBgNVHRMBAf8EAjAAMB0GA1Ud
DgQWBBRiSU9z7HlvY9XA3T51BSAQyNBwODAfBgNVHSMEGDAWgBSoSmpjBH3duubR
ObemRWXv86jsoTBvBggrBgEFBQcBAQRjMGEwLgYIKwYBBQUHMAGGImh0dHA6Ly9v
Y3NwLmludC14My5sZXRzZW5jcnlwdC5vcmcwLwYIKwYBBQUHMAKGI2h0dHA6Ly9j
ZXJ0LmludC14My5sZXRzZW5jcnlwdC5vcmcvMCEGA1UdEQQaMBiCFnd3dy5haXJm
b3JjZS1jYXNlcy5jb20wTAYDVR0gBEUwQzAIBgZngQwBAgEwNwYLKwYBBAGC3xMB
AQEwKDAmBggrBgEFBQcCARYaaHR0cDovL2Nwcy5sZXRzZW5jcnlwdC5vcmcwggEF
BgorBgEEAdZ5AgQCBIH2BIHzAPEAdwDwlaRZ8gDRgkAQLS+TiI6tS/4dR+OZ4dA0
prCoqo6ycwAAAW7VZEQEAAAEAwBIMEYCIQD2zG5R2ug1K3YDMb7Nus+2ijQvGT9A
CmIndnvMGHtt7QIhAKFuqZvDULsQSfbwmr/RONMlJJoqiOhpvf1AW0RTsxBeAHYA
B7dcG+V9aP/xsMYdIxXHuuZXfFeUt2ruvGE6GmnTohwAAAFu1WREMAAABAMARzBF
AiA0A/P4v9fK47oEIKSaO3MaNvBsyFbHf1t+xSyWD/tsBwIhAIi3xVKwkx1vSYCh
/zFHTcNu050toRG2YcQr/nMiWtvrMA0GCSqGSIb3DQEBCwUAA4IBAQCZ0okVrEoC
ARkvrPcmoCV3Fhn5k4+Ot03bbp2AQVf4Emg3TLcDfQHbyJTS8uCnfuodQx68+0g6
BtVIXUTywkkx2uUF2jq4o5/JbG/B9GaN1ve5HIyDyekJ/01z7KsUX1ckqJcFic9I
Lhn75XNRDAhR3Wk21u+Ekbofub1qVAChIJ/FY4Ig1IcmYSmNswd1igXKtBPi97Cm
tN2ZHyLAnFLxYgB2IxdUWvAUgTt0gPfV6spjvTcgd+kcRJLoFnwo+NXNPKwGQw0t
JZAe/FyGIeYA9MuYh8Z3BdH5M0q6scXqYwMCkv32M7P5R6Rx95zaT6f4iw+LxM4u
SPK0bwrDK9JK
-----END CERTIFICATE-----

Public Key (PEM)

-----BEGIN PUBLIC KEY-----
MIICIjANBgkqhkiG9w0BAQEFAAOCAg8AMIICCgKCAgEA4zaJq8haYwtARWjktPnd
vHYfjt85ISIYG1YDJYv004gcYgnWuhXx7vE9BaZX9ygOLgKVOFIpLT9Q7Cq6WtH5
kQhC3P80wkPAyh3gmEyQ8skttlJjdWoFGMi+2e2PQUAtVHxjzOiamnxdvATBpL+Y
qdtlycOrRJVXmHE1YVydYJgys/YstFRxzg6PiaEq2W11/0MfICgSGyp+mObMyq+P
wb66Y6FQ+9mMCM8BsglHH+ZQV/Yp703GjicP9qWqmmb3rPt7iPXQnBiRQoGrNKzF
fYcqXozxV/sz0LuFDNhRrTX8lS4EGTebU/XwxPgLMxiSMBmtenMjjAadiHNrgv6t
UF/uwDG9uiqv1ZCLEwiZYVEcnf+Pb+zyWhFrUKl6IksDBlSLQ3LoSFQ/S2WDm2tN
/af17Gr9dSAceuuxrEa9ptTGWdpyUxRUwbvYF8/vJ4EQ12XmbbfaeFm4LgQ0YTFy
zSM3X5CHmdvIlNyZBISob2wd2zRPU/7FF+r62VUMlYXJ49nzUOAxk3mRMkIHj8Zt
TIzfiHV+uGQpbcTm+jOvEdWPPEq+75jTmfJZAJ9vGM4wS6sZOzfJJi2D1VRsu8LX
QhSCkoMxP8REzdlpa1MtP8ZEheDsYsZV+SfHRUU3SlEnKsd6koFrt/aNA9GykpRM
CR0CmVjwZjjA6jk04lRduSECAwEAAQ==
-----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 276899225296555639757088998814124382188373
 . . . . . . . . [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 2019-12-05 08:29:08 +0000 UTC
 . . . . . . . . . . . . [c:0|t:23|false] UTCTime 2020-03-04 08:29:08 +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.airforce-cases.com'
 . . . . . . . . [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 926948323441491099143013028186774325221801632740798267280641735343353701591463911299548949072278635520230922992626255802915932806779446820037858893954672323246553691902207758887109854680280938477813865494932072099612962765620259017554263030618270486887131417259686705097859903874070613092905908408168395552293621273377902120360628280375768485592447048810179650240842388420503008054464603050505029056194258901423006495757545560358702141454119581219379115221895136083175371158248352195816878179366352566346596325328579672598474634994713325326606057560723193031440883934865042342676670633342696455425042189469648175302563282411193856068818580467680452535928872301027782672370364902148128052878172728584916041571366074499227289251244542559151655910069141742842507937843671902544616188820051081460105510789638553266732848763212051141140785183956556115101444290331683694704729888015275763850248333559802393529975950938896095834871256431712826584460319186184039291882826344255883578661433642359033605866484358235005381863527845931376544650813229357618224396594949925666330031026526239352066416233217658267068424079598247849696306437341089863765418351431741149132977274913914997245347417669565188426235416472314301273715274065736142681913633
 . . . . . . . . . . . . . . . . . . . . [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)
							62494f73ec796f63d5c0dd3e75052010c8d07038
 . . . . . . . . . . . . . . . . [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 (26 bytes)
 . . . . . . . . . . . . . . . . . . . . . . . . [c:0|t:16|true] SEQUENCE, SEQUENCE OF 
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . [c:2|t:2|false] IA5String 'www.airforce-cases.com'
 . . . . . . . . . . . . . . . . [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)
							00f1007700f095a459f200d18240102d2f93888ead4bfe1d47e399e1d034a6b0a8aa8eb2730000016ed56444040000040300483046022100f6cc6e51dae8352b760331becdbacfb68a342f193f400a6227767bcc187b6ded022100a16ea99bc350bb1049f6f09abfd138d325249a2a88e869bdfd405b4453b3105e00760007b75c1be57d68fff1b0c61d2315c7bae6577c5794b76aeebc613a1a69d3a21c0000016ed5644430000004030047304502203403f3f8bfd7cae3ba0420a49a3b731a36f06cc856c77f5b7ec52c960ffb6c0702210088b7c552b0931d6f4980a1ff31474dc36ed39d2da111b661c42bfe73225adbeb
 . . . . [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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