← Back to the reading view
Slides · 16 slides
Symmetric-key cryptography & AES
The same module told visually, ready to present. Speaker notes carry the full explanation.
Symmetric
Symmetric-key cryptography & AES
One shared key locks and unlocks the data, from disk encryption to the bulk of every TLS session
Symmetric-key cryptography & AES · Classical Crypto Today1 / 16
The model
One key, both directions
The whole scheme is only as safe as the key's secrecy
Symmetric-key cryptography & AES · Classical Crypto Today2 / 16
The workhorse operation
XOR undoes itself
Symmetric-key cryptography & AES · Classical Crypto Today3 / 16
Not encryption
Breaking single-byte XOR
Symmetric-key cryptography & AES · Classical Crypto Today4 / 16
The standard since 2001
AES at a glance
2¹²⁸ ≈ 3.4 × 10³⁸ candidate keys, and no attack beats brute force
Symmetric-key cryptography & AES · Classical Crypto Today5 / 16
Inside AES
Four steps, repeated
Symmetric-key cryptography & AES · Classical Crypto Today6 / 16
The 4×4 state
ShiftRows: row r moves left by r
Symmetric-key cryptography & AES · Classical Crypto Today7 / 16
Diffusion and keys
MixColumns and the key schedule
Round keys = rounds + 1, one for each AddRoundKey
Symmetric-key cryptography & AES · Classical Crypto Today8 / 16
Modes of operation
ECB leaks patterns
Symmetric-key cryptography & AES · Classical Crypto Today9 / 16
Advanced · ECB oracle
Byte-at-a-time ECB decryption
Symmetric-key cryptography & AES · Classical Crypto Today10 / 16
Chaining
CBC: each block feeds the next
Symmetric-key cryptography & AES · Classical Crypto Today11 / 16
Counter mode
CTR: AES as a keystream
No padding, fully parallel, random access
Symmetric-key cryptography & AES · Classical Crypto Today12 / 16
Authenticated encryption
GCM adds a tag to CTR
Symmetric-key cryptography & AES · Classical Crypto Today13 / 16
Block padding
PKCS#7: n bytes of value n
Symmetric-key cryptography & AES · Classical Crypto Today14 / 16
The catastrophic failure
Reuse a nonce and the keystream cancels
Symmetric-key cryptography & AES · Classical Crypto Today15 / 16
Post-quantum
AES survives quantum computers
Symmetric-key cryptography & AES · Classical Crypto Today16 / 16
1 / 16
Keys: ← → move, F full screen, G all slides, N notes