Certificate

References:

Table of contents

1. Certificate
   1. Attack
   2. TLS
   3. Digital Certificate
   4. RSA key
   5. X.509
      1. Signing Request
      2. Signing
      3. OCSP stapling

Attack

Threat Model:

• Ciphertext-only attack: have access only to the intercepted ciphertext
• Known-plaintext attack: knows some of the (plaintext, ciphertext) pairings
• Chosen-plaintext attack: intruder is able to obtain its corresponding ciphertext form

safety:

• confidentiality: eavesdrop
• integrity: alter attack, reordering attack
• authenticity: impersonate
• freshness (nonce): replay attack

TLS

1.client sends:

• a list of cryptographic algorithms it supports
• a client nonce.

2.server sends:

• a symmetric algorithm (for example, AES),
• a public key algorithm (for example, RSA with a specific key length)
• a MAC algorithm
• a certificate
• a server nonce.

3.client sends:

• a Pre-Master Secret (PMS), encrypted with public key
• Master Secret (MS): session MAC/encryption key for data sent from sever to client / client to server.

4.The client sends a MAC of all the handshake messages.

5.The server sends a MAC of all the handshake messages.

4,5 protect the handshake from tampering (downgrade attacking) (attacker may choose a weaker cryptographic algorithm)

Digital Certificate

• Domain Validated Certificates (DV / DVC)
  • X.509
  • typically used for TLS
  • Proves some control over a DNS domain
  • ideal for use on websites like this site that provides content, and not used for sensitive data.
• Extended Validation Certificate (EV / EVC)
  • used for HTTPS websites
  • proves the legal entity controlling the website or software package
  • requires verification of the requesting entity’s identity by a certificate authority (CA)

Type:

• fully qualified domain name (FQDN)
• Wildcard certificate: covers all sub domains under a particular domain name.
• SAN (Subject Alternative Name): secures 4 additional domain names in addition to the main domain name

RSA key

# generation
# #   If you want a non password protected key just remove the -des3 option
# #   -nodes: no password
openssl genrsa -des3 -out server.key 2048 

# remove passwd
openssl rsa -in server.key -out server_no_pwd.key

X.509

RFC 5280

File encoding:

• der: used for binary DER encoded certificates. It can bear
  • cer
  • crt
• pem: Base64-encoded with prefix -----BEGIN

File categories:

• crt: used for certificates. It may be encoded as der or pem.
• cer: The CER and CRT extensions are nearly synonymous. crt is commonly used among *nix systems while cer is a Microsoft conversion.
• key: used both for public and private PKCS#8 keys. It may be encoded as der or pem.

# inspection
openssl x509 -in cert.crt -text              # for pem encoding
openssl x509 -in cert.der -inform der -text  # for der encoding
openssl x509 -in cert.crt -outform der -out cert.der
openssl x509 -in cert.crt -inform der -outform pem -out cert.pem

# create CA certificate
#   may be used with -config
#   -nodes: no password
openssl req -x509 -days 365 -newkey rsa:4096 -sha256 -nodes -out cacert.pem
# or
openssl req -x509 -days 365 -new -key server.key -out cacert.pem -outform PEM

Signing Request

Typical information required:

a block of encoded text that is given to a Certificate Authority when applying for an SSL Certificate.

# inspection
openssl req -in server.csr -text

# creation
#   use -config to pass the information
openssl req -new -key server.key -out server.scr
openssl req -newkey rsa:4096 -sha256 -nodes -out server.scr

Signing

# sign
#   https://stackoverflow.com/questions/21297139/how-do-you-sign-a-certificate-signing-request-with-your-certification-authority
openssl ca -config openssl-ca.cnf -policy signing_policy -extensions signing_req -out servercert.pem -infiles servercert.csr
# openssl-ca.cnf
[ CA_default ]
base_dir      = .
certificate   = $base_dir/cacert.pem   # The CA certifcate
private_key   = $base_dir/cakey.pem    # The CA private key
new_certs_dir = $base_dir              # Location for new certs after signing
database      = $base_dir/index.txt    # Database index file         (e.g. 01)
serial        = $base_dir/serial.txt   # The current serial number   (e.g. 01)
unique_subject = no  # Set to 'no' to allow creation of
                     # several certificates with same subject.

# self-sign
openssl x509 -req -day 365 -in server.scr -signkey server.key -out server.crt

OCSP stapling

The Online Certificate Status Protocol (OCSP) stapling, formally known as the TLS Certificate Status Request extension, is a standard for checking the revocation status of X.509 digital certificates.

https://blog.cloudflare.com/high-reliability-ocsp-stapling/