Encryption Recap: A Refresher on Key Concepts

Encryption Recap: A Refresher on Key Concepts

DO and DON'T for developers

A while ago, I had chance to collect information and share this PDF summarizing common encryption terminology within my teams. This covers algorithms, and best practices that many developers may find helpful as a refresher or intro. Let me know if any part needs further explanation.

1. Data Encryption
Recap
Thomas Kim

2. Security &
Encryption
•Priority of security ‘was’ low than features
•There is NO 100% secure
•Security is not just cost, it is everything and
everywhere
•Encryption is the minimum defence, when
other security fails
•Encryption is minimum requirement for
any services or apps

3. Common
Terminology
•Number of Keys : Symmetric vs. Asymmetric
•Data Processing Unit : Stream vs. Block
•Data Recovery Capability : One Way vs. Both
Way

4. Hash
Functions
•Turn arbitrary size of input to fixed size of
output
•Guaranteed same output for same input
•It is fast, used for fast search as hash table
•Digest : output of hashing

5. Hash
Collision
•h(M) = H
•h() : hash function
•M : input
•H : hash (digest)
•Collision: different input,
same hash (MD5, SHA1)

6. Requirement of
Encrypting
Hash Function
•Pre-image Resistance
•2
nd Pre-image Resistance
•Collision Resistance

7. Pre-image
Resistance
With given hash H, difficult to find out original
input
h(M) = H
H = ‘aaf4c61ddcc5e8a2dabede0f3b482cd9aea9434d’
M = ‘hello’

8. 2
nd Pre-image
Resistance
With given (M), ensure there is no other
input (M`) to have the same h
h(M) = H
H = ‘aaf4c61ddcc5e8a2dabede0f3b482cd9aea9434d’
M = ‘hello’, M`=?

9. Collision
Resistance
•Ensure mathematically ‘nearly’ impossible
to have two M and M` that has same h
•Finding arbitrary M1, M2 that produce the
same h
•Stability of hash measured to the half of
the bit size of the algorithm (SHA1 =
80bit, SHA256 = 128bit)

10. Rainbow
Attack
•A type of Brute-force attack
•Using pre-calculated rainbow table to
match result H
•If H is the same, then M is out of the
rainbow table
•Prevent the attack by adding salt

11. Hashing
Algorithms
•MD5, SHA1, SHA2 (SHA256, SHA384, SHA512)
•MD5 (128bit) : not secure
•SHA1(160bit) : not recommended as long term
key (i.e. digital signature, used as one and only
algorithm for password encryption), still OK for
transient keys (session, git commit hash)

12. Symmetric-key
Algorithm
•One secret key for encryption and
decryption
•DES, 3DES, AES, IDEA, RC4, RC5
•Speedy and Easy to implement
•Hard to transfer secret keys each
other
•Key management is even harder
n(n-1)/2

13. Stream
Cipher
•Make a symmetric key
•Bit-wise XOR
•RC4, AS/2
•Speedy, no longer used

14. Block
Cipher
•encrypt/decrypt by data block
•symmetric algorithm
•DES : not recommended
•AES : adopted by NIST, 128/192/256
•Camellia : used for TLS session
•implementations by size of block
and key length
https://www.youtube.com/watch?v=gP4PqVGudtg

15. Padding
•Input data is NOT always the
multiples of block size
(i.e.) PKCS7/PKCS5 Padding : if lack
of 3 bytes, put 03 03 03

16. Mode of
Operations
•Define the rules between each blocks
•ECB, CBC, CFR, etc.

17. Mode of Operation
ECB
https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation
•Electronic Code Book
•No mode of operations
•Each block can be
encrypted/decrypted
•Critical issues (guess input)
•Shouldn’t be used with
symmetric key encryption
(i.e. AES/ECB NOT secure)

18. Mode of Operation
CBC
•Cipher Block Chaining
•Enhanced security
•Uses previous block as input to
produce the next block
•For 1st block, use IV
(Initialization Vector), hard to
guess
•Recommended for symmetric
key encryption (AES/CBC)
https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation

19. CBC
private static final String key = "aesEncryptionKey"; // 16 bytes
private static final String IV = "encryptionIntVec"; // 16 bytes
private static final String UTF8 = "UTF-8";

public static String encrypt(String value) {
try {
IvParameterSpec iv = new IvParameterSpec(IV.getBytes(UTF8));
SecretKeySpec spec = new SecretKeySpec(key.getBytes(UTF8), "AES");

Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5PADDING" );
cipher.init(Cipher.ENCRYPT_MODE, spec, iv);

byte[] encrypted = cipher.doFinal(value.getBytes());
return Base64.encodeBase64String(encrypted);
}
catch (Exception ex) {
ex.printStackTrace();
}
return null;
}
•Key : should be loaded
from secure storage
•IV : secure random value
•Key, IV are required for
encryption/decryption

20. Comparison
: Mode of Operations
•ECB
•CBC
ECB CBC
Original

21. PBKDF2
•Password Based Key Derivation Function 2
•Widely used for user password encryption
•Prevent brute-force attack by iteration (key
stretching)
1.Generate random key based on password
2.Adding salt
3.Iterate enough times to produce hash

22. Public Key
Encryption
•Asymmetric Key Algorithm
•Encrypt with Public Key
•Decrypt with Private Key
•Resolve the Difficulty of Key Sharing
•Used for
-Authentication
-Non-Repudiation
-Digital Signature

23. Public Key
Cryptography
RSA
•Rivest, Shamir, Adleman
•uses HUGE prime numbers as keys
•Much calculation, slow
ECDSA
•Elliptic Curve Digital Signature Algorithm
•Bitcoin
DSA
•Digital Signature Algorithm
13 = A * B
A=? and B=?
472,882,027 = A * B
A=? and B=?

24. Key
Exchange
•Key agreement
-Procedure to get agreement on key exchange
-Diffie-Hellman Algorithm (SSH, SSL)
(https://www.youtube.com/watch?v=wLFztjQDdzI )))
•Key Encipherment
-RSA Algorithm
1.Receiver generate symmetric key
2.Encrypt the symmetric key with sender’s public key
3.Transfer to the sender

25. SSL
TLS
•Session Key: symmetric key for a session
•SSL Hands-shake: key exchange procedure for SSL session
(Diffie-Hellman)
•SSL uses symmetric key (session key) throughout the session
•Session key cache for speed up
•TLS 1.2/1.3
•Excessive session timeout NOT recommended

26. PGP
•Pretty Good Privacy
•1991 by Phil Zimmermann
•Used for Email Encryption
•Public Key Repository (http://pgp.mit.edu)
•GPG Tools
•Lack of Certified Authority

27. CA
Certificate Authority
SSL
Certificate
SSL certificate issued by CA
•Public Key Certificate
•CA certify ownership of Public Key
•CA sign Public Key by its own Private Key
•validate SSL certificate by CA public key on establishing SSL session
•start to trust owner of SSL certificate certified by a CA
•Verification Domain Ownership by certificate chain
Self-Signed SSL Certificate
•certified by its own CA
•NO trust from browsers

28. Authentication
vs.
Authorization
Authentication
•validate a user (or entity) is right one
•By password, biometry (fingerprint, face/palm/
iris scan, voice signature), smart card, OTP, etc.
Authorization
•Decide whether allow or not (permission)
•Authentication followed by Authorization

29. HSM
Hardware Security Module
•Security Compliance
•Embedded circuit (or software) to perform
cryptographic calculation
•Key management
•No access of key from outside
•Self destroy keys on unauthorized
disassemble attempts*
•Keep information safe
•Cloud-based HSM available (AWS, Azure,
etc.)

30. Rules of
Thumb
PLEASE DON’T DO
•DO NOT try to invent new encryption algorithm by yourself
•DO NOT use AES/ECB, instead AES/CBC
•DO NOT save AES Keys and IVs as file
•DO NOT use Self-signed certificate (if possible)
PLEASE DO
•PBKDF2 for user password
•Use salt on one way hashing to avoid rainbow attack
•Use key stretching (hash iteration) to avoid brute-force attack
•Consider key strength and hash iteration based on life of data and importance
•Use HSM for Super sensitive data

31. Thanks
Q/A