What are the two basic functions used in encryption algorithms? - Essay Prowess

# What are the two basic functions used in encryption algorithms?

Part 1:

In no less than 250 words, explain the difference between symmetric and asymmetric encryption.  Which one is better and why?

Part 2:

2.1 What are the essential ingredients of a symmetric cipher?

2.2 What are the two basic functions used in encryption algorithms?

2.3 How many keys are required for two people to communicate via a symmetric cipher?

2.4 What is the difference between a block cipher and a stream cipher?

2.5 What are the two general approaches to attacking a cipher?

2.6 Why do some block cipher modes of operation only use encryption while others use both encryption and decryption?

2.7 What is triple encryption?

2.8 Why is the middle portion of 3DES a decryption rather than an encryption?

## solutions

1) Why symmetric key cryptography alone cannot resolveInternet security issue?

A ) Symmetric key algorithms are used primarily for the bulk encryption of data or data streams. These algorithms are designed to be very fast and have a large number of possible keys. The best symmetric key algorithms offer excellent secrecy; once data is encrypted with a given key, there is no fast way to decrypt the data without possessing the same key.

Symmetric key algorithms can be divided into two categories: block and stream. Block algorithms encrypt data a block (many bytes) at a time.

Cryptographic Strength of Symmetric Algorithms

Different encryption algorithms are not equal. Some systems are not very good at protecting data, allowing encrypted information to be decrypted without knowledge of the requisite key. Others are quite resistant to even the most determined attack. The ability of a cryptographic system to protect information from attack is called its strength. Strength depends on many factors, including:

• The secrecy of the
• The difficulty of guessing the key or trying out all possible keys (a key search). Longer keys are generally more difficult to guess or find.
• The difficulty of inverting the encryption algorithm without knowing the encryption key (breaking the encryption algorithm).
• The existence (or lack) of back doors, or additional ways by which an encrypted file can be decrypted more easily without knowing the
• The ability to decrypt an entire encrypted message if you know how a portion of it decrypts (called a known plaintext attack).
• The properties of the plaintext and knowledge of those properties by an attacker. For example, a cryptographic system may be vulnerable to attack if all messages encrypted with it begin or end with a known piece of plaintext. These kinds of regularities were used by the Allies to crack the German Enigma cipher during World War

In general, cryptographic strength is not proven; it is only disproven. When a new encryption algorithm is proposed, the author of the algorithm almost always believes that the algorithm offers "perfect" security ] that is, the author believes there is no way to decrypt an encrypted message without possession of the corresponding key. After all, if the algorithm contained a known flaw, then the author would not propose the algorithm in the first place (or at least would not propose it in good conscience).

Key Length with Symmetric Key Algorithms:

Among those who are not entirely familiar with the mathematics of cryptography, key length is a topic of continuing confusion. As we have seen, short keys can significantly compromise the security of encrypted messages because an attacker can merely decrypt the message with every

possible key to decipher the message's content. But while short keys provide comparatively little security, extremely long keys do not necessarily provide significantly more practical security than keys of moderate length. That is, while keys of 40 or 56 bits are not terribly secure, a key of 256 bits does not offer significantly more real security than a key of 168 bits, or even a key of 128 bits.

Inside a computer, a cryptographic key is represented as a string of binary digits. Each binary digit can be a 0 or a 1. Thus, if a key is 1 bit in length, there are two possible keys: 0 and 1. If a key is 2 bits in length, there are four possible keys: 00, 01, 10, and 11. If a key is 3 bits in length, there are eight possible keys: 000, 001, 010, 011, 100, 101, 110, and 111. In general, each added key bit doubles the number of keys. The mathematical equation that relates the number of possible keys to the number of bits is:

number of keys = 2(number of bits)

Data traded beginning with one schema then onto the following is guaranteed by system for encryption, a bestowed riddle key is used to encode and translate the data by the sender and gatherer separately. Such encryption is called symmetric key cryptography. There are various symmetric key counts which are attempted to be amazingly secure, yet the most concerning issue with this kind of schema is that the key must be bestowed over an open framework and all things considered it is predeployed on every sensor center point. Strayed key cryptography deals with issue, which can't be dictated by use of symmetric-key cryptography. In veered off key cryptography two keys are made, one private a bit of the key and exchange is called open key part. The private key is kept riddle while individuals by and large key is made open, the message is encoded using general social order key and the private key is used to interpret the message. An interchange wide utilization of such strategy is use of private key to sign the message, while

general social order key is used to check the signature at flip side. The most genuine issue joined with use of uneven cryptographic system is that it is moderate and outlandish. Regardless it incorporates key organization plan & progressed imprints to any framework to assurance hardened security.

B ) Why is it important to study the Feistel cipher

Feistel cipher using the concept of a product cipher, which is the performing of two or more basic ciphers in sequence in such a way that the final result or product is cryptographically stronger then any of the component ciphers.

Feistel proposed the use of a cipher that alternates substitutions and permutations. So Feistel cipher is considered to be an important one.

Most symmetric block encryption algorithms in current use are based on the Feistel block cipher structure. therefore, a study of the feistel structure reveals the principles

The central power of the strategy is to development a piece figure with a key length of "k" bits and a square length of "n" bits, allowing what indicated to "2k" possible progressions, instead of the "2n!" transformations receptive with the ideal square figure. Feistel proposed the use of an assume that substitutes substitutions and progressions. This is a practical demand to enhance a thing assume that exchan