ch5 Flashcards
(33 cards)
Cryptography
is the science of encrypting, or hiding, information—
* something people have sought to do since they began using language
Cryptographic algorithms (Ciphers)
are complicated methods of concealing
information by shifting letters around to make the text unreadable.
- is made up of mathematical steps for encrypting and decrypting information
Cryptanalysis
is the process of analyzing available information in an attempt
to return the encrypted message to its original form.
Plaintext
data to be protected
Ciphertext
Encrypted plaintext data
Key
secret data needed to encrypt/decrypt ciphertext
Encrypt/encode/encipher
plaintext → ciphertext
Decrypt/decode/decipher
ciphertext → plaintext
Cryptography is much more than encryption. Cryptographic methods
enable:
- Data protection
- Data hiding
- Integrity checks
- Nonrepudiation services
- Policy enforcement
- Key management and exchange
When you’re examining the strength of a cryptosystem, it is worth examining the following types of levels of protection / point must be consider when examining:
- The mechanism is no longer useful for any purpose.
- The cost of recovering the clear text without benefit of the key has fallen to a low
level. - The cost has fallen to equal to or less than the value of the data or the next leastcost attack.
- The cost has fallen to within several orders of magnitudes of the cost of encryption
or the value of the data. - The elapsed time of attack has fallen to within magnitudes of the life of the data,
regardless of the cost thereof. - The cost has fallen to less than the cost of a brute force attack against the key.
- Someone has recovered one key or one message
Cryptographic Operation include:
- Encryption (for the protection of confidentiality - protection against unauthorized
disclosure, i.e., only someone with the key can read the data) - Hashing (for the protection of integrity - protection against unauthorized modification,
i.e., only someone with the key can create or modify the data) - Digital signatures (to manage nonrepudiation)
- Key exchanges and other operations.
The methods used to encrypt information are based on two separate
operations:
- Substitution: is the replacement of one item with another item.
- Transposition: is the changing of the order of items.
The strength of a cryptographic algorithm depends on Several factors:
1- The Key size and the resulting keyspace (a set of possible key
values)
2- The work factor (a subjective measurement of the time and effort
needed to perform operations)
- If the work factor is low, then the rate at which keys can be tested
is high, meaning that larger keyspaces are needed.
Cryptographic methods exist for a purpose to protect the integrity and
confidentiality of data. There are many elements support this protection:
- Diffusion: is the principle that the statistical analysis of plaintext and
ciphertext results in a form of dispersion rendering one structurally
independent of the other. - Confusion: is a principle that affects the randomness of an output.
- Obfuscation: is the masking of an item to render it unreadable, yet still
usable. - Perfect Forward Secrecy: is a property of a public key system in which a key
derived from another key is not compromised even if the originating key is
compromised in the future. - Security Through Obscurity: is an approach to security using the mechanism
of hiding information to protect it.
Common Types of Encryption Algorithms:
- Hashing: takes an input and mathematically reduces it to a unique
number known as a hash, which is not reversible. - Symmetric: the same key is used for encryption and decryption.
- Asymmetric: uses two keys, a public key and a private key.
hash function
is a special mathematical
function that performs a one-way function to generate a message
summary for data integrity.
One-way function
means that once the algorithm is processed, there
is no feasible way to use the ciphertext to retrieve the plaintext that
was used to generate it
Hash value
is the output of the hashing algorithm for a specific input.
- A hash algorithm can be compromised with what is called a (collision attack), in which an attacker finds two different messages that hash to the same
value.
The Popular hash algorithms are in common use are:
- Message Digest (MD): hash of varying versions (MD2, MD4, MD5)
- Secure Hash Algorithm: series (SHA-1, SHA-2, SHA-3)
Symmetric Encryption
** check p13
- older and simpler method of encrypting information.
- both the sender and the
receiver of the message have previously obtained the same key.
- based on this shared secret principle,
including the unbreakable one-time pad method.
Two requirements for secure use of symmetric encryption:
- a strong encryption algorithm
- a secret key known only to sender / receiver
Y = E^K(X)
X = D^K(Y)
Asymmetric encryption / Asymmetric object
is a public/private keypair encryption used for authentication, nonrepudiation, and confidentiality.
Asymmetric cryptography uses pair of keys:
- a private key that is kept secret
- a public key that can be sent to anyone.
Public key applications can be classified into 3 categories:
- encryption/decryption (provide secrecy)
- digital signatures (provide authentication)
- key exchange (of session keys)
