# Difference Between Public Key Cryptography And Private Key Cryptography Pdf

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- The difference between Encryption, Hashing and Salting
- Asymmetric Encryption
- asymmetric key cryptography pdf
- Asymmetric Encryption

## The difference between Encryption, Hashing and Salting

Public-key cryptography , or asymmetric cryptography , is a cryptographic system which uses pairs of keys : public keys which may be known to others , and private keys which may never be known by any except the owner.

The generation of such key pairs depends on cryptographic algorithms which are based on mathematical problems termed one-way functions. Effective security requires keeping the private key private; the public key can be openly distributed without compromising security.

In such a system, any person can encrypt a message using the intended receiver's public key , but that encrypted message can only be decrypted with the receiver's private key. This allows, for instance, a server program to generate a cryptographic key intended for a suitable symmetric-key cryptography , then to use a client's openly-shared public key to encrypt that newly-generated symmetric key.

The server can then send this encrypted symmetric key over an insecure channel to the client; only the client can decrypt it using the client's private key which pairs with the public key used by the server to encrypt the message.

With the client and server both having the same symmetric key, they can safely use symmetric key encryption likely much faster to communicate over otherwise-insecure channels. This scheme has the advantage of not having to manually pre-share symmetric keys a fundamentally difficult problem while gaining the higher data throughput advantage of symmetric-key cryptography.

With public-key cryptography, robust authentication is also possible. A sender can combine a message with a private key to create a short digital signature on the message. Anyone with the sender's corresponding public key can combine that message with a claimed digital signature; if the signature matches the message, the origin of the message is verified i.

Public key algorithms are fundamental security primitives in modern cryptosystems , including applications and protocols which offer assurance of the confidentiality, authenticity and non-repudiability of electronic communications and data storage. Some public key algorithms provide key distribution and secrecy e. Compared to symmetric encryption , asymmetric encryption is rather slower than good symmetric encryption, too slow for many purposes.

Today's cryptosystems such as TLS , Secure Shell use both symmetric encryption and asymmetric encryption. Before the mids, all cipher systems used symmetric key algorithms , in which the same cryptographic key is used with the underlying algorithm by both the sender and the recipient, who must both keep it secret.

Of necessity, the key in every such system had to be exchanged between the communicating parties in some secure way prior to any use of the system — for instance, via a secure channel.

This requirement is never trivial and very rapidly becomes unmanageable as the number of participants increases, or when secure channels aren't available, or when, as is sensible cryptographic practice , keys are frequently changed.

In particular, if messages are meant to be secure from other users, a separate key is required for each possible pair of users. By contrast, in a public key system, the public keys can be disseminated widely and openly, and only the corresponding private keys need be kept secret by its owner.

There are several possible approaches, including:. A public key infrastructure PKI , in which one or more third parties — known as certificate authorities — certify ownership of key pairs. TLS relies upon this. This implies that the PKI system software, hardware, and management is trust-able by all involved.

A " web of trust " which decentralizes authentication by using individual endorsements of links between a user and the public key belonging to that user. The DKIM system for digitally signing emails also uses this approach. The most obvious application of a public key encryption system is for encrypting communication to provide confidentiality — a message that a sender encrypts using the recipient's public key which can be decrypted only by the recipient's paired private key.

Another application in public key cryptography is the digital signature. Digital signature schemes can be used for sender authentication. Non-repudiation systems use digital signatures to ensure that one party cannot successfully dispute its authorship of a document or communication. Further applications built on this foundation include: digital cash , password-authenticated key agreement , time-stamping services , non-repudiation protocols, etc. The initial asymmetric cryptography-based key exchange to share a server-generated symmetric key from the server to client has the advantage of not requiring that a symmetric key be pre-shared manually, such as on printed paper or discs transported by a courtier, while providing the higher data throughput of symmetric key cryptography over asymmetric key cryptography for the remainder of the shared connection.

As with all security-related systems, it is important to identify potential weaknesses. Aside from poor choice of an asymmetric key algorithm there are few which are widely regarded as satisfactory or too short a key length, the chief security risk is that the private key of a pair becomes known.

All security of messages, authentication, etc, will then be lost. All public key schemes are in theory susceptible to a " brute-force key search attack ". In many cases, the work factor can be increased by simply choosing a longer key. But other algorithms may inherently have much lower work factors, making resistance to a brute-force attack eg, from longer keys irrelevant. Some special and specific algorithms have been developed to aid in attacking some public key encryption algorithms — both RSA and ElGamal encryption have known attacks that are much faster than the brute-force approach.

Major weaknesses have been found for several formerly promising asymmetric key algorithms. The "knapsack packing" algorithm was found to be insecure after the development of a new attack. These are often independent of the algorithm being used. Research is underway to both discover, and to protect against, new attacks.

Another potential security vulnerability in using asymmetric keys is the possibility of a "man-in-the-middle" attack , in which the communication of public keys is intercepted by a third party the "man in the middle" and then modified to provide different public keys instead.

Encrypted messages and responses must, in all instances, be intercepted, decrypted, and re-encrypted by the attacker using the correct public keys for the different communication segments so as to avoid suspicion.

A communication is said to be insecure where data is transmitted in a manner that allows for interception also called " sniffing ". These terms refer to reading the sender's private data in its entirety.

A communication is particularly unsafe when interceptions can't be prevented or monitored by the sender. A man-in-the-middle attack can be difficult to implement due to the complexities of modern security protocols. However, the task becomes simpler when a sender is using insecure media such as public networks, the Internet , or wireless communication. In these cases an attacker can compromise the communications infrastructure rather than the data itself.

A hypothetical malicious staff member at an Internet Service Provider ISP might find a man-in-the-middle attack relatively straightforward. Capturing the public key would only require searching for the key as it gets sent through the ISP's communications hardware; in properly implemented asymmetric key schemes, this is not a significant risk. In some advanced man-in-the-middle attacks, one side of the communication will see the original data while the other will receive a malicious variant.

Asymmetric man-in-the-middle attacks can prevent users from realizing their connection is compromised. This remains so even when one user's data is known to be compromised because the data appears fine to the other user. This can lead to confusing disagreements between users such as "it must be on your end! Hence, man-in-the-middle attacks are only fully preventable when the communications infrastructure is physically controlled by one or both parties; such as via a wired route inside the sender's own building.

In summation, public keys are easier to alter when the communications hardware used by a sender is controlled by an attacker. One approach to prevent such attacks involves the use of a public key infrastructure PKI ; a set of roles, policies, and procedures needed to create, manage, distribute, use, store and revoke digital certificates and manage public-key encryption. However, this has potential weaknesses. For example, the certificate authority issuing the certificate must be trusted by all participating parties to have properly checked the identity of the key-holder, to have ensured the correctness of the public key when it issues a certificate, to be secure from computer piracy, and to have made arrangements with all participants to check all their certificates before protected communications can begin.

Web browsers , for instance, are supplied with a long list of "self-signed identity certificates" from PKI providers — these are used to check the bona fides of the certificate authority and then, in a second step, the certificates of potential communicators.

An attacker who could subvert one of those certificate authorities into issuing a certificate for a bogus public key could then mount a "man-in-the-middle" attack as easily as if the certificate scheme were not used at all. In an alternative scenario rarely discussed [ citation needed ] , an attacker who penetrates an authority's servers and obtains its store of certificates and keys public and private would be able to spoof, masquerade, decrypt, and forge transactions without limit.

Despite its theoretical and potential problems, this approach is widely used. Examples include TLS and its predecessor SSL , which are commonly used to provide security for web browser transactions for example, to securely send credit card details to an online store. Aside from the resistance to attack of a particular key pair, the security of the certification hierarchy must be considered when deploying public key systems. Some certificate authority — usually a purpose-built program running on a server computer — vouches for the identities assigned to specific private keys by producing a digital certificate.

Public key digital certificates are typically valid for several years at a time, so the associated private keys must be held securely over that time. When a private key used for certificate creation higher in the PKI server hierarchy is compromised, or accidentally disclosed, then a " man-in-the-middle attack " is possible, making any subordinate certificate wholly insecure. During the early history of cryptography , two parties would rely upon a key that they would exchange by means of a secure, but non-cryptographic, method such as a face-to-face meeting, or a trusted courier.

This key, which both parties must then keep absolutely secret, could then be used to exchange encrypted messages. A number of significant practical difficulties arise with this approach to distributing keys. Can the reader say what two numbers multiplied together will produce the number ?

Here he described the relationship of one-way functions to cryptography, and went on to discuss specifically the factorization problem used to create a trapdoor function. In July , mathematician Solomon W. Golomb said: "Jevons anticipated a key feature of the RSA Algorithm for public key cryptography, although he certainly did not invent the concept of public key cryptography.

In , James H. Ellis , a British cryptographer at the UK Government Communications Headquarters GCHQ , conceived of the possibility of "non-secret encryption", now called public key cryptography , but could see no way to implement it.

Williamson , developed what is now known as Diffie—Hellman key exchange. I judged it most important for military use Only at the end of the evolution from Berners-Lee designing an open internet architecture for CERN , its adaptation and adoption for the Arpanet These discoveries were not publicly acknowledged for 27 years, until the research was declassified by the British government in In , an asymmetric key cryptosystem was published by Whitfield Diffie and Martin Hellman who, influenced by Ralph Merkle 's work on public key distribution, disclosed a method of public key agreement.

This method of key exchange, which uses exponentiation in a finite field , came to be known as Diffie—Hellman key exchange. Merkle's "public key-agreement technique" became known as Merkle's Puzzles , and was invented in and only published in The latter authors published their work in in Martin Gardner 's Scientific American column, and the algorithm came to be known as RSA , from their initials. Its security is connected to the extreme difficulty of factoring large integers , a problem for which there is no known efficient general technique though prime factorization may be obtained through brute-force attacks; this grows much more difficult the larger the prime factors are.

A description of the algorithm was published in the Mathematical Games column in the August issue of Scientific American.

Since the s, a large number and variety of encryption, digital signature, key agreement, and other techniques have been developed, including the Rabin cryptosystem , ElGamal encryption , DSA - and elliptic curve cryptography.

From Wikipedia, the free encyclopedia. Cryptographic system with public and private keys. This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. Cryptography and Network Security: Principles and Practice. Prentice Hall. Menezes, Paul C.

## Asymmetric Encryption

Public-key encryption. Asymmetric encryption, also known as public-key encryption, is a form of data encryption where the encryption key also called the public key and the corresponding decryption key also called the private key are different. A message encrypted with the public key can be decrypted only with the corresponding private key. The public key and the private key are related mathematically, but it is computationally infeasible to derive the private key from the public key. Therefore, a recipient could distribute the public key widely. Anyone can use the public key to encrypt messages for the recipient and only the recipient can decrypt them. A public-key encryption algorithm requires a trapdoor one-way function, i.

Quick, do you know the difference between encryption and hashing? Do you know what salting is? Do you think salting your hash is just part of an Irish breakfast? Oftentimes without any explanation. Encryption is the practice of scrambling information in a way that only someone with a corresponding key can unscramble and read it.

Cryptography is the science of secret writing with the intention of keeping the data secret. Cryptography is classified into symmetric cryptography, asymmetric cryptography and hashing. Private Key : In Private key, the same key secret key is used for encryption and decryption. In this key is symmetric because the only key is copy or share by another party to decrypt the cipher text. It is faster than the public key cryptography. Public Key : In Public key, two keys are used one key is used for encryption and another key is used for decryption.

Computationally infeasible to determine private key PK ➢Encryption: given plaintext M and public key PK, Eavesdropper can't tell the difference between.

## asymmetric key cryptography pdf

Public-key cryptography , or asymmetric cryptography , is a cryptographic system which uses pairs of keys : public keys which may be known to others , and private keys which may never be known by any except the owner. The generation of such key pairs depends on cryptographic algorithms which are based on mathematical problems termed one-way functions. Effective security requires keeping the private key private; the public key can be openly distributed without compromising security. In such a system, any person can encrypt a message using the intended receiver's public key , but that encrypted message can only be decrypted with the receiver's private key. This allows, for instance, a server program to generate a cryptographic key intended for a suitable symmetric-key cryptography , then to use a client's openly-shared public key to encrypt that newly-generated symmetric key.

Public-key cryptography, or asymmetric cryptography, is a cryptographic system that uses pairs of keys: public keys, which may be disseminated widely, and private keys, which are known only to the owner. This preview shows page 1 - 4 out of 15 pages. The main difference between symmetric and asymmetric encryption is that the symmetric encryption uses the same key for both encryption and decryption while the asymmetric encryption uses two different keys for encryption and decryption..

*Since that time, this paper has taken on a life of its own Does increased security provide comfort to paranoid people? Or does security provide some very basic protections that we are naive to believe that we don't need?*

### Asymmetric Encryption

In ECC a black key is generated directly on hardware. Few mathematics t… Slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. Explanation and proof of RSA algorithm in details.

Public-key cryptography, or asymmetric cryptography, is an encryption scheme that uses two mathematically related, but not identical, keys - a public key and a private key. Unlike symmetric key algorithms that rely on one key to both encrypt and decrypt, each key performs a unique function. The public key is used to encrypt and the private key is used to decrypt. It is computationally infeasible to compute the private key based on the public key.

Private Key is used to both encrypt and decrypt the data and is shared between the sender and receiver of encrypted data. The public key is only used to encrypt data and to decrypt the data, the private key is used and is shared.

#### Information Center Articles

The main difference between public key and private key in cryptography is that the public key is used for data encryption while the private key is used for data decryption. The public key and private key are two locking mechanisms used in asymmetric encryption of cryptography. Public key is a type of lock used with an encryption algorithm to convert the message to an unreadable form. Private key is a type of lock used with a decryption algorithm to convert the received message back to the original message. Both these keys help to ensure the security of the exchanged data. In brief, a message encrypted with the public key cannot be decrypted without using the corresponding private key.

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