Certificate chain

Certificate chain also known as certification path is the list of certificates used to authenticate the subject. The path starts with the subject’s certificate. Each level up is identified by “Issuer” filed of the certificate. This is the case until we reach the root CA certificate. This certificate is signed by the root CA itself as it is at the top of the hierarchy. Certificate chain allows us to verify the whole trust chain. If any of the certificates in the path fails validation the end certificate cannot be trusted.

Graphic sourced from: http://publib.boulder.ibm.com/infocenter/wmqv6/v6r0/index.jsp?topic=%2Fcom.ibm.mq.csqzas.doc%2Fsy10600_.htm

Certificate issued to an endpoint. Issued by the subordinate CA IssuingCA-DC1.kp.local

Subordinate CA certificate issued by ORCA1-CA

Root CA certificate issued and signed by the CA itself

It is important to note that whether certificate chain is checked depends on the implementation of the application. While most of applications and operating systems validate the path some do not. For example some versions of Android don't check the path. We should always test to ensure expected results.

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x.509 Certificates - Critical vs non-critical extensions

Extensions are used to associate additional information with the user or the key. Each certificate extension has three attributes - extnID, critical, extnValue extnID - Extension ID - an OID that specifies the format and definitions of the extension critical - Critical flag - Boolean value extnValue - Extension value Criticality flag specifies whether the information in an extension is important. If an application doesn't recognize the extension marked as critical, the certificate cannot be accepted. If an extension is not marked as critical (critical value False) it can be ignored by an application. In Windows, critical extensions are marked with a yellow exclamation mark, View certificate extensions using OpenSSL: # openssl x509 -inform pem -in cert.pem -text -noout (output abbreviated) X509v3 extensions: X509v3 Key Usage: critical Digital Signature, Key Encipherment X509v3 Subject Key Identifier

DNS response and error types

In this post we explore common DNS response codes. We will cover the following responses: NOERROR SERVFAIL NXDOMAIN NODATA REFUSED Throughout article we’ll refer to the following RFCs: RFC 1034 - DOMAIN NAMES - CONCEPTS AND FACILITIES RFC 2308 - Negative Caching of DNS Queries (DNS NCACHE) RFC 2136 - Dynamic Updates in the Domain Name System (DNS UPDATE) RFC 8914 - Extended DNS Errors Response Codes - RCODEs The DNS RCODES are best defined in RFC2316 . They signify what type of response was sent by the server. “RCODE Response code - this four bit field is undefined in requests and set in responses.” The table below shows the summary of the currently defined RCODEs. Mnemonic Val Description NOERROR 0 No error condition.

Count number of lines - 'findstr'

How do I count number of lines in a command output? findstr /r/n "^" | find /c ":" Above commands will display number of lines output by whatever command (well, nearly whatever) you specify in the front. For example: C:\>ping localhost | findstr /r/n "^" | find /c ":" FINDSTR: // ignored 12 This comes handy if you want to find out how many OUs you have in Active Directory: dsquery ou -limit 0 | findstr /r/n "^" | find /c ":" How many user accounts there are: dsquery user -limit 0 | findstr /r/n "^" | find /c ":" Computers: dsquery computer -limit | findstr /r/n "^" | find /c ":"

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