Crypto 101 pdf
Authentication: The process of proving one's identity. Integrity: Assuring the receiver that the received message has not been altered in any way from the original. Non-repudiation: A mechanism to prove that the sender really sent this message. Key exchange: The method by which crypto keys are shared between sender and receiver.
In cryptography, we start with the unencrypted data, referred to as plaintext. Plaintext is encrypted into ciphertext, which will in turn usually be decrypted back into usable plaintext. The encryption and decryption is based upon the type of cryptography scheme being employed and some form of key.
Given this, there are other functions that might be supported by crypto and other terms that one might hear: Forward Secrecy aka Perfect Forward Secrecy : This feature protects past encrypted sessions from compromise even if the server holding the messages is compromised. This is accomplished by creating a different key for every session so that compromise of a single key does not threaten the entirely of the communications. Perfect Security: A system that is unbreakable and where the ciphertext conveys no information about the plaintext or the key.
To achieve perfect security, the key has to be at least as long as the plaintext, making analysis and even brute-force attacks impossible. One-time pads are an example of such a system. Deniable Authentication aka Message Repudiation : A method whereby participants in an exchange of messages can be assured in the authenticity of the messages but in such a way that senders can later plausibly deny their participation to a third-party.
In many of the descriptions below, two communicating parties will be referred to as Alice and Bob; this is the common nomenclature in the crypto field and literature to make it easier to identify the communicating parties. If there is a third and fourth party to the communication, they will be referred to as Carol and Dave, respectively. A malicious party is referred to as Mallory, an eavesdropper as Eve, and a trusted third party as Trent.
Finally, cryptography is most closely associated with the development and creation of the mathematical algorithms used to encrypt and decrypt messages, whereas cryptanalysis is the science of analyzing and breaking encryption schemes.
Cryptology is the umbrella term referring to the broad study of secret writing, and encompasses both cryptography and cryptanalysis. For purposes of this paper, they will be categorized based on the number of keys that are employed for encryption and decryption, and further defined by their application and use. The three types of algorithms that will be discussed are Figure 1 : Secret Key Cryptography SKC : Uses a single key for both encryption and decryption; also called symmetric encryption.
Primarily used for privacy and confidentiality. Public Key Cryptography PKC : Uses one key for encryption and another for decryption; also called asymmetric encryption. Primarily used for authentication, non-repudiation, and key exchange. Hash Functions: Uses a mathematical transformation to irreversibly "encrypt" information, providing a digital fingerprint. Primarily used for message integrity. Secret Key Cryptography Secret key cryptography methods employ a single key for both encryption and decryption.
As shown in Figure 1A, the sender uses the key to encrypt the plaintext and sends the ciphertext to the receiver. The receiver applies the same key to decrypt the message and recover the plaintext. Because a single key is used for both functions, secret key cryptography is also called symmetric encryption. With this form of cryptography, it is obvious that the key must be known to both the sender and the receiver; that, in fact, is the secret.
The biggest difficulty with this approach, of course, is the distribution of the key more on that later in the discussion of public key cryptography. Secret key cryptography schemes are generally categorized as being either stream ciphers or block ciphers. A Self-synchronizing stream cipher. From Schneier, , Figure 9. Stream ciphers operate on a single bit byte or computer word at a time and implement some form of feedback mechanism so that the key is constantly changing.
Stream ciphers come in several flavors but two are worth mentioning here Figure 2. Self-synchronizing stream ciphers calculate each bit in the keystream as a function of the previous n bits in the keystream. It is termed "self-synchronizing" because the decryption process can stay synchronized with the encryption process merely by knowing how far into the n-bit keystream it is. One problem is error propagation; a garbled bit in transmission will result in n garbled bits at the receiving side.
Synchronous stream ciphers generate the keystream in a fashion independent of the message stream but by using the same keystream generation function at sender and receiver. While stream ciphers do not propagate transmission errors, they are, by their nature, periodic so that the keystream will eventually repeat. Source: Wikimedia Commons A block cipher is so-called because the scheme encrypts one fixed-size block of data at a time.
In a block cipher, a given plaintext block will always encrypt to the same ciphertext when using the same key i. The most common construct for block encryption algorithms is the Feistel cipher , named for cryptographer Horst Feistel IBM. As shown in Figure 3, a Feistel cipher combines elements of substitution, permutation transposition , and key expansion; these features create a large amount of " confusion and diffusion " per Claude Shannon in the cipher.
One advantage of the Feistel design is that the encryption and decryption stages are similar, sometimes identical, requiring only a reversal of the key operation, thus dramatically reducing the size of the code or circuitry necessary to implement the cipher in software or hardware, respectively. One of Feistel's early papers describing this operation is " Cryptography and Computer Privacy " Scientific American, May , 5 , Block ciphers can operate in one of several modes; the following are the most important: Electronic Codebook ECB mode is the simplest, most obvious application: the secret key is used to encrypt the plaintext block to form a ciphertext block.
Two identical plaintext blocks, then, will always generate the same ciphertext block. ECB is susceptible to a variety of brute-force attacks because of the fact that the same plaintext block will always encrypt to the same ciphertext , as well as deletion and insertion attacks. In addition, a single bit error in the transmission of the ciphertext results in an error in the entire block of decrypted plaintext.
Cipher Block Chaining CBC mode adds a feedback mechanism to the encryption scheme; the plaintext is exclusively-ORed XORed with the previous ciphertext block prior to encryption so that two identical plaintext blocks will encrypt differently. While CBC protects against many brute-force, deletion, and insertion attacks, a single bit error in the ciphertext yields an entire block error in the decrypted plaintext block and a bit error in the next decrypted plaintext block.
Cipher Feedback CFB mode is a block cipher implementation as a self-synchronizing stream cipher. CFB mode allows data to be encrypted in units smaller than the block size, which might be useful in some applications such as encrypting interactive terminal input.
If we were using one-byte CFB mode, for example, each incoming character is placed into a shift register the same size as the block, encrypted, and the block transmitted. At the receiving side, the ciphertext is decrypted and the extra bits in the block i. CFB mode generates a keystream based upon the previous ciphertext the initial key comes from an Initialization Vector [IV]. In this mode, a single bit error in the ciphertext affects both this block and the following one.
Output Feedback OFB mode is a block cipher implementation conceptually similar to a synchronous stream cipher. OFB prevents the same plaintext block from generating the same ciphertext block by using an internal feedback mechanism that generates the keystream independently of both the plaintext and ciphertext bitstreams. In OFB, a single bit error in ciphertext yields a single bit error in the decrypted plaintext.
Counter CTR mode is a relatively modern addition to block ciphers. Unlike ECB, however, CTR uses different key inputs to different blocks so that two identical blocks of plaintext will not result in the same ciphertext. Finally, each block of ciphertext has specific location within the encrypted message. DES is a Feistel block-cipher employing a bit key that operates on bit blocks. What are the risks to using cryptocurrency? Cryptocurrencies are still relatively new, and the market for these digital currencies is very volatile.
Since cryptocurrencies don't need banks or any other third party to regulate them; they tend to be uninsured and are hard to convert into a form of tangible currency such as US dollars or euros. In addition, since cryptocurrencies are technology-based intangible assets, they can be hacked like any other intangible technology asset.
Finally, since you store your cryptocurrencies in a digital wallet, if you lose your wallet or access to it or to wallet backups , you have lost your entire cryptocurrency investment. Follow these tips to protect your cryptocurrencies: Look before you leap! Before investing in a cryptocurrency, be sure you understand how it works, where it can be used, and how to exchange it. Read the webpages for the currency itself such as Ethereum , Bitcoin or Litecoin so that you fully understand how it works, and read independent articles on the cryptocurrencies you are considering as well.
Use a trustworthy wallet. It is going to take some research on your part to choose the right wallet for your needs. If you choose to manage your cryptocurrency wallet with a local application on your computer or mobile device, then you will need to protect this wallet at a level consistent with your investment.
Just like you wouldn't carry a million dollars around in a paper bag, don't choose an unknown or lesser-known wallet to protect your cryptocurrency.
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Novel hash functions, encryption algorithms and pseudorandom number generators based on chaotic systems for electronic commerce are proposed. The securities of the proposed algorithms are analyzed based on some well-know statistical tests in this filed.
In additi on, a new one-dimensional triangle-chaotic map TCM with perfect chaotic behaviour is presented. We have compared the proposed chaos-based hash functions, block cipher and pseudorandom number generator with well-know algorithms. The comparison results show that the proposed algorithms are better than some other existing algorithms. Several analyses and computer simulations are performed on the proposed algorithms to verify their characteristics, confirming that these proposed algorithms satisfy the characteristics and conditions of security algorithms.
In Cryptography in. NET Succinc The international symposium MQC addresses the mathematics and quantum theory underlying secure modeling of the post quantum cryptography including e. Defend Dissent Defend Dissent is an introduction to cryptography paired with the social impacts of surveillance and the protective potential of encryption, with a focus on US social movements.
Each chapter ends with a story that brings social context to the material - from surveillance used against contemporary US protests to the African National Congress's Platform Embedded Security Technology Revealed Platform Embedded Security Technology Revealed is an in-depth introduction to Intel's platform embedded solution: the security and management engine. The engine is shipped inside most Intel platforms for servers, personal computers, tablets, and smartphones.
The engine realizes advanced security and management functionalities and protects appl
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The securities of the proposed algorithms are analyzed based on some well-know statistical tests in this filed. In additi on, a new one-dimensional triangle-chaotic map TCM with perfect chaotic behaviour is presented. We have compared the proposed chaos-based hash functions, block cipher and pseudorandom number generator with well-know algorithms. The comparison results show that the proposed algorithms are better than some other existing algorithms.
Several analyses and computer simulations are performed on the proposed algorithms to verify their characteristics, confirming that these proposed algorithms satisfy the characteristics and conditions of security algorithms. The proposed algorithms in this thesis are high-potential for adoption in e-commerce applications and protocols. In Cryptography in. NET Succinc The international symposium MQC addresses the mathematics and quantum theory underlying secure modeling of the post quantum cryptography including e.
Defend Dissent Defend Dissent is an introduction to cryptography paired with the social impacts of surveillance and the protective potential of encryption, with a focus on US social movements. Each chapter ends with a story that brings social context to the material - from surveillance used against contemporary US protests to the African National Congress's Platform Embedded Security Technology Revealed Platform Embedded Security Technology Revealed is an in-depth introduction to Intel's platform embedded solution: the security and management engine.
The engine is shipped inside most Intel platforms for servers, personal computers, tablets, and smartphones. The engine realizes advanced security and management functionalities and protects appl
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