MOD 20 - Cryptography Flashcards
Types of ciphers:
Symmetric, Asymmetric, Substitution, Transposition, Stream, Block. Be familiar with each of these.
Be familiar with encryption processes, PKI, digital signatures, non-repudiation, public & private keys, certificates, CA’s, RA’s, CRL’s, etc.
Certificate Validation
Process of checking a certificate to ensure it’s valid and has not been revoked
Symmetric ciphers:
Only one key: the same key encrypts and decrypts. MUCH faster than Asymmetric, so used for any bulk-encryption needs
The main drawback to symmetric is there is no built-in way to exchange the key with the recipient.
RC4 (Ron’s Code 4) SYM
Symmetric STREAM cipher used in WEP and WPA/TKIP
DES - Data Encryption Standard SYM
Uses 56-bit keys and 64-bit blocks
2DES SYM
does DES twice, with 2 different keys. Susceptible to a “Meet-in-the-Middle” attack, allowing the attacker to figure out 1 of the keys.
3DES SYM
does DES three times, with 3 different keys (oversimplified, but that’s the idea)
Twofish SYM
Uses 128 bit blocks, and up to 256 bit key size.
Threefish SYM
Blocks and keys can be 256, 512, and 1024 bits
AES - Advanced Encryption Standard SYM
Currently our best symmetric encryption option. Like Twofish, it uses 128 bit blocks and 128, 192, or 256 bit keys. Faster than Twofish!
AES is a block cipher and when used with WPA2 we call it CCMP (AES in CTR mode)
- CAST-128 SYM
Symmetric block cipher that uses 64-bit blocks and does 12 or 16 rounds of encryption
- Serpent SYM
Symmetric block cipher that uses four 32-bit blocks, does 32 rounds of encryption, and uses key sizes of 128, 192, or 256 bits
IDEA (used with PGP) SYM
Symmetric encryption that was supposed to replace DES. Optionally used with PGP for bulk encryption once RSA handles the key-exchange. 64 bit blocks, 128 bit key.
Asymmetric ciphers:
Creates a Public-Private key pair. Encrypt with either one, then only the OTHER one can decrypt.
RSA (Rivest, Shamir, Adleman) ASYM
First creates a private key, then mathematically deduces a public key from the private key, which is a one-way math function (can’t be reversed)
ECC (Elliptic Curve Cryptography) ASYM
Can use small keys, but then get’s large-strength encryption from them. Very useful for portable devices with weaker processors.
Hashing algorithms:
Can be used to see if files (any data really) have changed. Used as an INTEGRITY checking mechanism.
MD5 (Message Digest 5) HASH ALG
32 (hex) character output, which is 128 bits. Prone to collisions
SHA-1 (Secure Hashing Algorithm 1) HASH ALG
40 (hex) char output, 160 bits. Very similar to MD5, but more bits means less collisions.
Collisions
Problem with hashing where two (or more) different source messages produce the same message digest.
Collision resistance is the ability for a hashing algorithm to produce less collisions. This typically involves a very long digest (more bits means more unique digests)
A collision attack is an attempt to find two messages that produce the same hash. While not all that practical, it does demonstrate that a particular hashing algorithm is flawed. SHA-1 and MD5 are prone to these attacks.
Key Escrow
In general, NEVER give your private key to anyone! The only exception is if you want your administrator to back up your private key for safekeeping. The admin’s role is then called the Recovery Agent (or Data Recovery Agent), and she keeps your private key in a safe location we call Key Escrow.
PGP (Pretty Good Privacy)
Program that can encrypt data such as e-mails. Uses RSA for symmetric-key-exchange, then IDEA for the bulk data encryption. Free for 30 days, but you have to pay after that.
For data confidentiality, encrypt with recipients Public Key
Only the recipients private can decrypt
*GPG
GNU Privacy Guard. Free alternative/competitor to PGP
- Web-of-Trust
Security model used by PGP/GPG/etc where each user acts as a CA and signs each other’s public keys for distribution. Every user has a “ring of public keys” (other users keys) to encrypt data and keep it confidential.
TPM - Trusted Platform Module
“Crypto-chip” on your motherboard that can generate and store encryption keys. Can be used with tools like Bitlocker, which can encrypt/decrypt data on your hard disk. Microsoft’s Bitlocker tool can do disk encryption.
DROWN attack
Your webserver allows inbound TLS connections using a certificate (public key) and corresponding private key. Unfortunately, your server is mis-configured and still allows SSL v2 connections. In this scenario, the very same certificate and private key are being used for both the TLS and SSL connections. The problem here is that SSL v2 has known vulnerabilities that can let an attacker get your webserver’s private key. Once he does, since your server uses the same cert for both TLS and SSL v2, the attacker can now intercept and view your incoming TLS traffic. Solution: disable SSL!!
- Heartbleed
High-profile vulnerability with the SSL protocol (from 2014) that exposed a webserver’s PRIVATE key
Allowed attacker to get web server PRIVATE KEY. SSL 3.0 was hacked.
Cryptanalysis
Breaking encryption. An ADAPTIVE chosen plaintext (or ciphertext) attack allows the attacker to make many interactive queries to encrypt his/her data, then he/she is able to choose subsequent plaintexts based on the results of the previous encryption.
Rubber-Hose attack
Getting someone’s encryption key through coercion or torture. Not recommended.
*Key Stretching
Process of strengthening a key by making it longer
Difference between Digital Signature and Asymmetric
Know these. Digital signature only proves nonrepudiation, does not provide confidentiality. Use senders private key.
For confidentiality, encrypt with recipients public
Dual-Key-Pair
Encrypts header and digital signs with senders private, then encrypts the data with recipients public, decrypts with private. Receiver uses public key to decrypt hash.
Certificate Authority
Vouches for a public key by signing it.
Registration Authority
Verifies user is authentic. May perform background check. Like GoDaddy, Digicert
Recovery Agent or Data Recovert Agent
Special Admin role tasked with backing up employee private keys.
Key Escrow
Secure location for the DRA to store/back-up employee’s private keys
Adaptive chosen plain text attack
Attacker makes a series of interactive queries, choosing subsequent plain texts based on the information
DUHK Attack
Don’t Use Hard-Coded Keys
