Encryption

• in cryptography, it is the process of encoding a message that provides:
  • message confidentiality - where authorized parties can decode it & unauthorized parties cannot decode it

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Cryptographic Hash Function
Message Digest Function

• is a hash function with the following properties:
  • pre-image resistance - given ℎ𝑎𝑠ℎ-𝑣𝑎𝑙𝑢𝑒, it is infeasible to find 𝑥 such that 𝐻(𝑥)=ℎ𝑎𝑠ℎ-𝑣𝑎𝑙𝑢𝑒
  • weak collision resistance - given 𝑥, it is infeasible to find 𝑦 such that 𝐻(𝑦)=𝐻(𝑥)
  • strong collision resistance - it is infeasible to find any 𝑥,𝑦 such that 𝐻(𝑦)=𝐻(𝑥)
• cryptographic hash functions are not used for:
  • encryption
  • authentication
  • digital signature generation (a digital signature verifies the authenticity and integrity of a message). This is because cryptographic hash functions use no secret/private keys to generate hashes. For enforcing integrity and authentication, use Asymmetric-Key Functions or Keyed Hash Functions

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Keyed Cryptographic Hash Function

• utilizes a cryptographic hash function and a secret cryptographic key for either:
  • encryption - for message confidentiality
  • HMAC - for message authenticity/integrity (HMAC is a hash-based form of MIC)
• secure hash functions generating HMACs could be used in place of “digital signatures”, but does not protect against non-repudiation (where 1 of the 2 parties that share the same key could secretly sign a message and say it was signed from the other)

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MIC

MICs are sometimes incorrectly referred as Digital Signatures

• both enforce integrity and authenticity
• both use cryptographic keys

the difference is that:

• Digital Signatures use asymmetric-key functions
• MICs use symmetric-key functions
  • Hash-Based MACs use keyed cryptographic hash functions

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Digital Signatures

• a digital signature of a message (which is produced by the signer) gives a recipient very strong reason to ensure:
  • message authentication - message originated from the stated signer
  • message integrity - message has not been changed

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Message Authentication Code (MAC)
Message Integrity Code (MIC)

• used to ensure:
  • message authentication - the message came from the stated sender
  • message integrity - the message has not been changed

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MIC & Encryption

utilizing both:

• MIC or HMAC - is a short piece of info used to provide authentication/integrity of a message
• encryption - is encoding a message to provide confidentiality

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Error - Detection & Correction

• error detection - is the detection of errors caused by noise or other impairments during transmission from the transmitter to the receiver
• error correction - is the automatic correction of errors that arise from the incorrect transmission of digital data

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Cryptocurrency - Crypto Currency

• is a digital asset designed to work as a medium of exchange that uses strong cryptography to secure financial transactions, control the creation of additional units, and verify the transfer of assets

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iO)

• In cryptography, indistinguishability obfuscation is a type of software obfuscation with the defining property that obfuscating any two programs that compute the same mathematical function results in programs that cannot be distinguished from each other
• Currently, known indistinguishability obfuscation candidates are very far from being practical. As measured by a 2017 paper, even obfuscating the toy function which outputs the logical conjunction of its thirty-two Boolean data type inputs produces a program nearly a dozen gigabytes large

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