Cryptography Exam – Comprehensive Practice
Questions & Exam Preparation
History of Cryptography • From the Greek words
kryptos, meaning “hidden”, and
graphein, meaning “to write”.
• Literally secret writing.
Cryptography Designing systems such as encryption and digital signatures
Cryptoanalysis Breaking systems such as encryption, digital signatures
Cryptology A science that covers both the concepts of cryptography and
cryptoanalysis.
Encryption Converts a "plaintext" into an encoded text or a "ciphertext"
, Decryption The reverse of Encryption
Cipher Algorithms used to encrypt and decrypt text
Key An unknown parameter needed to operate a particular
cipher's algorithms
Goal of Crypto - Protect information (e.g., devices, applications, documents)
- Ensure security of communication over insecure medium
- Communicate even with possibility of adversary
The Principle of Encryption - Plaintext is encrypted using a key
- Ciphertext is decrypted using the same key
Ingredients of a Cryptosystem m -> Message or (Plain) text
m -> _________ c c -> Cipher text produced by Ek(m)
-> __________ k - k -> Key
>___________ Ek - Ek -> Cryptographic Transformation (one-to-one mapping)
>_________ Dk - Dk -> Inverse of Ek (viz. Dk(Ek(m)) = m)
>_________
Possible Attack Types 1.Ciphertext-only attack
2.Known-plaintext attack
3.Chosen-plaintext attack
4.Chosen-ciphertext attack
Ciphertext-only attack The adversary knows:
- a ciphertext c
- the underlying encryption algorithm
Known-plaintext attack The adversary knows:
- the encryption algorithm
- One or more plaintext -ciphertext pairs formed with the
secret key: (m1,c1), (m2,c2), ..., (mk,ck)
- a new ciphertext c
Chosen-plaintext attack The adversary can choose:
- the encryption algorithm
- -(m1,c1), (m2,c2), ..., (mk,ck), where m1, m2, ..., mk are chosen by
the adversary
- a new ciphertext c
Chosen-ciphertext attack The adversary can choose
-the encryption algorithm
-(m1,c1), (m2,c2), ..., (mk,ck), where c1, c2, ..., ck are chosen by the
adversary
-a new ciphertext c
A Good Cryptographic Algorithm This resists ciphertext-only and known-plaintext attacks
Questions & Exam Preparation
History of Cryptography • From the Greek words
kryptos, meaning “hidden”, and
graphein, meaning “to write”.
• Literally secret writing.
Cryptography Designing systems such as encryption and digital signatures
Cryptoanalysis Breaking systems such as encryption, digital signatures
Cryptology A science that covers both the concepts of cryptography and
cryptoanalysis.
Encryption Converts a "plaintext" into an encoded text or a "ciphertext"
, Decryption The reverse of Encryption
Cipher Algorithms used to encrypt and decrypt text
Key An unknown parameter needed to operate a particular
cipher's algorithms
Goal of Crypto - Protect information (e.g., devices, applications, documents)
- Ensure security of communication over insecure medium
- Communicate even with possibility of adversary
The Principle of Encryption - Plaintext is encrypted using a key
- Ciphertext is decrypted using the same key
Ingredients of a Cryptosystem m -> Message or (Plain) text
m -> _________ c c -> Cipher text produced by Ek(m)
-> __________ k - k -> Key
>___________ Ek - Ek -> Cryptographic Transformation (one-to-one mapping)
>_________ Dk - Dk -> Inverse of Ek (viz. Dk(Ek(m)) = m)
>_________
Possible Attack Types 1.Ciphertext-only attack
2.Known-plaintext attack
3.Chosen-plaintext attack
4.Chosen-ciphertext attack
Ciphertext-only attack The adversary knows:
- a ciphertext c
- the underlying encryption algorithm
Known-plaintext attack The adversary knows:
- the encryption algorithm
- One or more plaintext -ciphertext pairs formed with the
secret key: (m1,c1), (m2,c2), ..., (mk,ck)
- a new ciphertext c
Chosen-plaintext attack The adversary can choose:
- the encryption algorithm
- -(m1,c1), (m2,c2), ..., (mk,ck), where m1, m2, ..., mk are chosen by
the adversary
- a new ciphertext c
Chosen-ciphertext attack The adversary can choose
-the encryption algorithm
-(m1,c1), (m2,c2), ..., (mk,ck), where c1, c2, ..., ck are chosen by the
adversary
-a new ciphertext c
A Good Cryptographic Algorithm This resists ciphertext-only and known-plaintext attacks
