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OpenSSL

Section 1

Section 2

What is SSL/TLS? What is HTTPS?

The internet is many routers owned by many different ISPs.

  • On either end: you and who you are speaking to

Most common data transferred on the internet is websites,

  • Written in HTML (Hyper Text Markup Language)
  • Transferred with: HTTP (Hyper Text Transfer Protocol)

SSL / TLS create a secure, protected tunnel across the internet - HTTP - HTML transferred with HTTP protected by SSL.

  • SSL / TLS can also protect other data transfer
    • SSL VPN
  • SSL - Secure Sockets Layer
    • created by Netscape
  • TLS - Transport Layer Security
    • IETF renamed protocol to TLS

How do SSL/TLS Protect Your Data?

Data sent across a wire can be captured by anyone in the middle. The purpose of SSL/TLS is to protect the data in three ways:

  • Confidentiality - data is only accessible by client and server -> Encryption
  • Integrity - data is not modified between the client and server -> Hashing
  • Authentication- client/server are indeed who they are they are -> PKI

Anti-Replay and Non-Repudiation

Anti-Replay

  • Provided with built-in sequence numbers
  • Built into integrity + authentication mechanism

Non-Repudiation

  • Repudiate - to refuse to have anything to do with
  • Sender cannot later deny sending a message
  • Byproduct of integrity + authentication

Key Players

Client

  • Entity initiating the TLS handshake
  • Web browser
    • Phone, apps, smart toaster, IOT...
  • Optionally authenticated (rare)

Server

  • Entity receiving the TLS handshake
    • Web server
      • Apache, IIS, NGINX, etc...
      • Load balancer or SSL Accelerator
  • Always authenticated

Certificate Authority

  • Governing entity that issues certificates
  • Trusted by client and server
  • Provides trust anchor
    • If we trust the CA, we trust what the CA trusts
  • Five organizations secure 98% of the internet:
    • IdenTrust (51.9%)
      • Let's Encrypt
    • DigiCert (19.4%)
      • Verisign
    • Sectigo (17.5%)
    • GoDaddy (6.9%)
    • GlobalSign (2.9%)

Hashing

Algorithm which takes as input a message of arbitrary length and produces as output a "fingerprint" fof the original message.

  • "hello" -> 8 + 5 + 12 + 12 + 15
  • Hashing is often referred to one-way encryption
  • Result of the hashing algorithm is called a digest
    • Also called: checksum, fingerprint, hash, CRC, etc...
  • Real world hashing algorithms must satisfy four requirements:
    • Infeasible to produce given digest
    • Impossible to extract original message
    • Slight changes to produce drastic differences
    • Resulting digest is fixed width (length)

Example:

echo "hello" | md5sum

Collisions

  • Two messages result in identical digests
  • Cannot be avoided - It is a byproduct of "fixed width digests"

Common hashing algorithms:

  • MD5 - 128 bits
  • SHA/SHA1 - 160 bits
  • SHA2 family:
    • SHA-224 - 224 bits
    • SHA-256 - 256 bits
    • SHA-384 - 384 bits
    • SHA-512 - 512 bits

Data Integrity

Hashing is used to provide integrity.

  • Sender calculates digest from the message
  • Sender sends message digest
  • Receiver calculates digest from the received message
  • Receiver compares both digests
    • If the digests are identical, the message was not modified in transit
    • However, simply hashing the message is not enough. The MIM can intercept message, modify the message, recalculate digest and then send both to receiver.
  • Both parties establish a mutual secret key
  • Sender combines messages + secret key to create digest
  • Receiver verifies by calculating hash of message + secret key
  • Message Authentication Code (MAC)
    • Concept of combining message + secret key when calculating digest
    • Provides integrity and authentication for bulk data transfer
    • Message + secret key must be combined in the same way
    • Industry standard implementation of MAC: HMAC
      • Hash Based Message Authentication Code (RFC 2104)

Encryption

Encryption if used to provide confidentiality.

  • Plain text: data before encryption
  • Cipher text: data while encryption

Simple encryption: transforms plain text into cipher text.

Key Based Encryption:

  • Combines industry vetted algorithm with a secret key
    • Algorithms is created by experts
    • Secret keys can be randomly generated

Two types of Key Based Encryption:

  • Symmetric Encryption
    • Encrypt and decrypt using the same keys
    • Ideal for bulk data
    • Strength:
      • Faster. Lower CPU cost.
      • Cipher text is same size as plain text
    • Weakness:
      • Secret key must be shared - less secure
    • DES, RC4, 3DES, AES, ChaCha20
  • Asymmetrical Encryption
    • Encrypt and decrypt using different keys
    • These two keys are mathematically related
    • What one key encrypts, only the other can decrypt
    • Restricted to limited data
    • One key will be made public, other key will be kept private
    • Weaknesses:
      • Slower. Requires much larger key sizes.
      • Cipher text expansion
    • Strengths:
      • Private key is never shared - more secure
    • DSA, RSA, Diffie-Hellman, ECDSA, ECDH

Public and Private Keys

Example 1:

  • Jim wants to send a secret message to Pam
  • Jim uses Pam's public key to encrypt the message
  • Only the correlating private key can decrypt

Example 2:

  • Pam wants to prove that she sent the message

  • Pam uses her private key to encrypt the message

  • If Jim can decrypt Pam's public key:

    • Jim knows Pam must have sent the message
    • Jim knows message was not modified in transit

  • Asymmetric Key Pairs can provide encryption and signatures

  • But what if we used asymmetric keys to share symmetric keys?

Example 3:

  • Pam randomly generates a symmetric secret key
  • Pam encrypts symmetric key with Jim's public key
  • Jim decrypts symmetric key with Jim's private key
  • Bulk data can now be symmetrically encrypted
    • This can be done in either direction, for arbitrary amount of data
  • Hybrid Encryption - concept of using both asymmetric and symmetric encryption
    • Asymmetric encryption to facilitate key exchange
    • Secret key used with symmetrical encryption for bulk data

Example 4:

  • Process for using an asymmetrical key pair for signatures:
  • Pam calculates a hash of a message
  • Pam encrypts a hash of a message
  • Jim decrypts the signature with Pam's public key
  • Jim calculates hash of received message
  • If both digests, match, this proves two things:
    • Message hasn't changed since Pam signed it
    • Only Pam could have created the signatures

How TLS/SSL Use Cryptography

CA is trusted by client. CA will generate a certificate. Certificate links an asymmetric key pair to a specific identity. Certificate is signed by the CA (provides authentication).

PKI

Three entities form a PKI: client, server, CA. The client is the entity that needs to connect securely to something or to verify a particular identity. The server is the entity that needs to prove its identity. The Certificate Authority is the governing entity which verifies identities and generates certificates. There could also be a corporate PKI.

RSA (Rivest Shamir and Edelman)

RSA is by far the most popular asymmetric encryption algorithm in use today. RSA creates a pair of commutative keys:

  • i.e. encrypt with one of the keys and decrypt with the other; it doesn't matter which order you go in.

DH/DSA work differently:

  • Semi-prime numbers are numbers that are divisible by prime numbers
  • RSA Example:
    • Generating keys:
      • Select two prime numbers (P, Q) - 7, 19
      • Calculate product (P * Q) - 133
      • Calculate totient (P - 1) * (Q - 1) - 108
      • Select public key (E) - 29
        • Must be prime
        • Must be less than totient
        • Must NOT be a factor of the totient
      • Select private key (D) - 41
        • Product of D and E, divided by T must result in a remainder of 1
        • (D * E) % T = 1
    • Encryption and Decryption
      • Encryption:
        • message ^E^ % N = cipher text
      • Decryption:
        • cipher ^D^ % N = message
    • Encrypt with public key, decrypt with private key (works both ways)
      • 60^29^ % 133 = 86
      • 8g^41^ % 133 = 60
      • 60^41^ % 133 = 72
      • 72^29^ % 133 = 60
    • How secure is RSA?
      • Security lies in difficulty of factoring prime numbers
      • If given 133, could you extract 7 and 19?
      • How about 1909?
      • In 1991, RSA Labs created the RSA Challenge. They released 54 different semi-private numbers of various sizes and offered cash prizes for anybody that could drive the prime factors.
        • The competition ended in 2007 and only 12 of the original 54 had been solved
        • As of 2020, another 11 were solved
        • The biggest semi prime that was factored was 829 bits
        • In the almost 30 years since these numbers were originally published, the 1024 bit number that they released has never been factored
        • 2048 bit RSA keys is the standard since 2015

Diffie Helman (DH)

Allows two parties to establish a shared secret over an unsecured medium. Shared secrets is never transmitted. Security of DH is dependent on discrete logarithm problem.

Digital Signature Algorithm (DSA)

DSA is a asymmetric encryption algorithm. DSA simply creates and validates signatures.

  • No encryption, no key exchange

DSA simply has two operations:

  • Signature generation
    • Input: message, private key, random #, dsa params
    • Output: signature
  • Signature verification:
    • Input: message, public key, signature, dsa params
    • Output: true or false
  • Random numbers is very important
    • Must be unique for each message or DSA fails catastrophically
    • If random numbers is ever re-used, private key can be extracted
    • RFC 6969 - generate random number deterministically based on message

Section 3

Generating and Inspecting RSA Keys

Generate 1024 bit RSA key:

  • openssl genrsa -out RSA-key1.pem 1024

Inspect RSA key:

  • openssl rsa -in RSA-key1.pem -text

Inspect RSA key without pem format:

  • openssl rsa -in RSA-key1.pem -text - noout

Generate 4096 bit RSA private key, encrypted with AES128:

  • safer if transferring it
  • openssl genrsa -out RSA-key2.pem -aes128 4096
  • des is insecure by today's standards

List all algorithms:

  • openssl list -cipher-algorithms

Generating and Inspecting DSA Keys

Generate DSA parameters file

  • openssl dsaparam -out DSA-PARAM.pem 1024

Generate DSA keys file with parameters file

  • openssl gendsa -out DSA-key.pem DSA-PARAM.pem

Generate DSA Parameters and Keys in one File

  • openssl dsaparam -genkey -out DSA-PARAM-KEY.pem 2048

Inspecting DSA Parameters file

  • openssl dsaparam -in DSA-PARAM.pem -text -noout

Inspecting DSA Private Key file

  • openssl dsa -in DSA-KEY.pem -text -noout

Generating and Inspecting Elliptical Curve Keys

Generate EC Parameters file

  • openssl genpkey -genparam -algorithm EC -pkeyopt ec_paramgen_curve:secp384r1 -out EC-PARAM.pem

Generate EC Keys from Parameters file

  • openssl genpkey -paramfile EC-PARAM.pem -out EC-KEY.pem

Generate EC Keys directly

  • openssl genpkey -algorithm EC -pkeyopt ec_paramgen_curve:P-384 -out EC-KEY.pem

View supported Elliptic Curves

  • openssl ecparam -list_curves
  • Recommended Curves: prime256v1, secp384r1, secp521r1 (identical to P-256, P-384, P-521)

Inspecting Elliptic Curve (EC) Parameters file

  • openssl ecparam -in EC-PARAM.pem -text -noout

Inspecting Elliptic Curve (EC) Private Key file

  • openssl ec -in EC-KEY.pem -text -noout

Section 4

Adding and Removing Encryption to RSA Keys

Removing encryption from an RSA key file

  • openssl rsa -in ENCRYPTED-KEY.pem -out KEY.pem

Encrypting an RSA Key File

  • `openssl rsa -in KEY.pem -aes128 -out ENCRYPTED-KEY.pem``

Hash a RSA key

  • sha1sum RSA-key1.pem

OpenSSL PKey Utility

Converting any Private Key file into text (RSA, DSA, or EC)

  • openssl pkey -in KEY.pem -noout -text

Extracting only Public Key as text from any Key file

  • openssl pkey -in KEY.pem -noout -text_pub

Extracting only Public Key in PEM format

  • openssl pkey -in KEY.pem -pubout

pkey expects a Private Key file. Public Key file can be read with -pubin

Matching Private Keys to Certificates and CSRs

Check if RSA Key matches a CSR or Cert

  • Compare Modulus values to see if files match each other
    • openssl req -in CSR.pem -noout -modulus
    • openssl x509 -in CERT.pem -noout -modulus
    • openssl rsa -in KEY.pem -noout -modulus

Check if EC Key matches a CSR or Cert

  • Compare Public Key values to see if files match each other
    • openssl req -in EC-CSR.pem -noout -pubkey
    • openssl x509 -in EC-CERT.pem -noout -pubkey
    • openssl ec -in EC-KEY.pem -pubout

Section 5

Generating Certificate Signing Requests (CSRs) and Self-Signed Certificates

Generating CSRs:

  • Generate CSR with existing Private Key file
    • openssl req -new -key KEY.pem -out CSR.pem
  • Generate CSR and new Private Key file
    • openssl req -new -newkey <alg:opt> -nodes -out CSR.pem

Generating Self-Signed Certificates:

  • Generate Certificate with existing Private Key file
    • openssl req -x509 -key KEY.pem -out CERT.pem
  • Generate Certificate and new Private Key file
    • openssl req -x509 -newkey <alg:opt> -nodes -out CERT.pem

Self-signed certificates will have the same subject and issuer.

Section 6

Extracting Specific Information From Certificates and CSRs

Viewing x509 Certificate as human readable Text

  • openssl x509 -in CERT.pem -noout -text

Viewing Certificate Signing Request (CSR) contents as Text:

  • openssl req -in CSR.pem -noout -text

Extract specific pieces of information from x509 Certificates

  • openssl x509 -in CERT.pem -noout -dates
  • openssl x509 -in CERT.pem -noout -issuer –subject

Other items you can extract:

-modulus -pubkey -ocsp_uri -ocspid
-serial -startdate -enddate

Section 7

To check if file is PEM format

  • openssl x509 -in FILE

To check if file is DER format

  • openssl x509 -in FILE -inform DER`

To check if file is PFX format

  • openssl pkcs12 -in FILE -nodes

To check, or convert, PEM or DER Key Files use openssl pkey instead of openssl x509 and same command arguments.

Convert PEM Certificate file to DER

  • openssl x509 -in CERT.pem -outform DER -out CERT.der

Convert DER Certificate file to PEM

  • openssl x509 -in CERT.der -inform der -out CERT.pem

Convert PEM Certificate(s) to PFX

  • openssl pkcs12 -in CERTS.pem -nokeys -export -out CERTS.pfx

To include a key in PFX file use -inkey KEY.pem instead of -nokeys.

To extract everything within a PFX file as a PEM file:

  • openssl pkcs12 -in FILE.pfx -out EVERYTHING.pem -nodes

To extract only the Private Key from a PFX file as PEM:

  • openssl pkcs12 -in FILE.pfx -out KEY.pem -nodes -nocerts

PFX files can contain Certificate(s), or Certificate(s) + one matching Key

  • -clcerts - extract only end-entity certificate (client certificate)
  • -cacerts - extract all but end-entity certificate
  • -nokeys - extract only certficiates

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