1. X.690:
   1. An ITU-T standard specifying several ASN.1 encoding formats:
      1. ITU-T X.690 Encoding Formats:
         1. # Basic Encoding Rules (BER):
            1. The original ruleset governing the encoding of ASN.1 data structures.
         2. # Canonical Encoding Rules (CER):
            1. A restricted version of BER
            2. If chosen, only CER may be used. All other formats are restricted.
         3. # Distinguished Encoding Rules (DER):
            1. Another restricted variant of BER
            2. If chosen, only DER may be used. All other formats are restricted.
            3. Note: Files are DER encoded, NOT necessarily .DER extension; DER encoded certificates may be .DER, .CER, or .CRT
            4. Has restrictive TLV sorting rules
            5. Base2 (binary)
            6. Widely used for X.509 certificates. For example, certificate enrollment in Windows Servers uses DER exclusively.
   2. The syntax defines TLV encoding elements:
      1. Type identifier
      2. Length description
      3. Value (Contents)
2. Privacy-Enhanced Mail (PEM):
   1. Uses the DER encoding method
   2. Base64 (ASCII) encoded DER certificate file extension.
   3. The .PEM extension is used for X.509v3 files which contain Base64 (ASCII) data.
   4. All .PEM armored data is prefixed/suffixed between "-----BEGIN CERTIFICATE-----" and "-----END CERTIFICATE-----"
3. The original X.509 standards were never broadly adopted. Instead, they were overtaken by these two standards:
   1. Pretty Good Privacy (PGP)
   2. Secure Multipurpose Internet Mail Extensions (S/MIME)
4. Public Key Cryptography Standards (PKCS):
   1. A set of standards devised and published by RSA Security beginning in the early 1990s to promote their patented cryptography techniques.
   2. Although they are not industry standards like IETF or PKIX, their ratings still hold relevance due to the widespread use of their algorithms.
   3. All algorithms not listed have either been abandoned, or are beyond the scope of this test:
      1. PKCS#1: RSA Cryptography Standard
      2. PKCS#3: Diffie-Hellman Key Agreement Standard
      3. PKCS#5: Password-Based Encryption Standard
      4. PKCS#7: Cryptographic Message Syntax Standard
         1. Digital ID S/MIME format file.
         2. See RFC 2315 for more information.
      5. PKCS#8: Private Key Information Syntax Standard
      6. PKCS#10: Certification Request Syntax Specification
      7. PKCS#12: Personal Information Exchange Syntax Standard
         1. A file format able to store multiple password-protected and/or encrypted certificates.
         2. P12 format files are often used to establish client authentication certificates.
         3. See RFC 7292 for more information.