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Cryptography

Cryptography refers to the science of rendering information unrecognizable and thus useless to those without proper authorization. This field includes mathematics, computer science and engineering. While cryptography was initially applied to protect message confidentiality, it has grown to include issues such as privacy concerns, data integrity, identity authentication, secure computing and more. This article introduces the field of cryptography, defines the basic concepts of encryption and decryption and discusses related concepts. It also explores current uses of cryptography in the information security field.

Encryption/Decryption

Cryptography is used to protect the confidentiality of data. When original data (referred to as plaintext) is transformed cryptographically, it is encrypted, or disguised. The process of encryption produces ciphertext, or cipher. The ciphertext is not readable until it is converted back into plaintext through a process called decryption. The process of decryption can only be initiated by the designated recipient through the use of a key. Examples of ciphertext include substituting letters for numbers, rotating letters of the alphabet, scrambling voice signals, or using computer algorithms to rearrange data bits in digital signals.

The most secure encryption methods rely on mathematical algorithms and a key (or password) for decryption. The key is a variable value, often a random character string, which is necessary for transforming the ciphertext back into plaintext. The key is known only by authorized individuals and should not be shared with other parties.

Encryption and decryption are crucial elements in a number of other processes, including:

  • Authentication: this process verifies or establishes the identity of an entity or of the data. User authentication verifies if a user is authorized to enter a system. This is based on three factors of identification: something the user knows (e.g. PIN, password); something the user has (e.g. ID card, smart card, token); or something the user is or does (e.g. biometric identifiers). Data authentication establishes both data integrity and data origin authentication.
  • Data confidentiality: this ensures that sensitive data is kept secure. Data confidentiality may involve data that is transmitted between two parties, through intermediaries, or data that is kept in repositories. Ensuring data confidentiality means that sensitive information is not accessed by attackers or other unauthorized parties.
  • Data origin authentication: this confirms that the sender of the data is the originator of the data, rather than someone claiming to be the originator.
  • Data integrity: a high level of data integrity assures users that the information is trustworthy, complete and untampered with. Data integrity ensures that data is accessible, correct and consistent.

There are a number of different levels of encryption, which depend on the key space. The key space refers to the number of possible keys that may be used to initialize an algorithm. Organizations can choose from different levels, depending on their requirements:

  1. File-Level Encryption: this encrypts data at the individual file level. Users can decide which files to encrypt, depending on the sensitivity of their contents. This method is also referred to as folder encryption, since entire folders can be encrypted in a similar fashion. Files are encrypted and decrypted by users who have been authenticated.
  2. Full-Drive Encryption: this method encrypts all the data that is on the disk drive. This is done through software on the hard disk driver, or by the hardware in the disk drive. Users must be authenticated when the disk drive is powered on, before they can gain access to the data.
  3. Field-Level Encryption: this method encrypts only designated fields in a document. The non-encrypted fields are then able to appear in plaintext when viewed.

Non-Repudiation & Digital Signatures

Cryptography influences non-repudiation, which proves that the integrity and origin of data is genuine. Repudiation is when one party involved in a communication denies involvement in some or all of the communication. Users need to have evidence that messages were sent. This prevents a sender from later denying having sent a message. Non-repudiation falls under two categories:

  1. Proof of Origin: Non-repudiation with proof of origin establishes the origin of the data, protecting the recipient in case the sender should deny sending the data. This ensures accountability from the originating party. Often, the term “non-repudiation” is used interchangeably with non-repudiation with proof of origin.
  2. Proof of Receipt: Non-repudiation with proof of receipt proves that the data was received as it was originally addressed. This protects the sender in case the recipient should deny receipt of the data.

There are a number of ways to ensure non-repudiation. For instance, a data hash can establish, to a reasonable degree, that the data was not manipulated without detection. Data hashes, or hash functions, convert large amounts of data into single integers. However, data hashes cannot prevent data from being manipulated during the transmission process.

Another way to ensure non-repudiation is to use digital certificates. Digital certificates confirm that information transmitted electronically is authentic. For instance, digital certificates may be used for e-commerce, online banking and other sensitive online services. In these situations, encryption is insufficient; certificates are necessary as evidence of the sender of the encrypted information.

Digital certificates associate an identity to a pair of electronic keys for encryption of digital information. They make it possible to verify a claim to identity and prevent impersonation. Digital certificates usually contain the following:

  • Owner’s public key
  • Owner’s name
  • Expiration date of the public key
  • Name of issuer – this is the certification authority that issued the certificate
  • Serial number of the certificate
  • Digital signature of the issuer

Symmetric & Asymmetric Encryption

There are two types of encryption schemes: symmetric encryption and asymmetric encryption.

Symmetric key cryptography refers to using the same key for encrypting as well as decrypting. It is also referred to as shared secret, secret-key or private key. This key is not distributed, rather is kept secret by the sending and receiving parties. With symmetric encryption, the sender encrypts a plaintext message with a symmetric encryption algorithm and a shared key. This process results in a ciphertext message that is sent to the recipient. The recipient then decrypts this message back as a plaintext with a shared key. With this form of encryption, the two parties must share the key over a secure channel before communications.

Asymmetric cryptography is also referred to as public-key cryptography. Public key depends on a key pair for the processes of encryption and decryption. Unlike private keys, public keys are distributed freely and publicly. Data that has been encrypted with a public key can only be decrypted with a private key.

Asymmetric cryptography is the most recent cryptographic technique. With asymmetric cryptography, the sender encrypts a plaintext message with an asymmetric encryption algorithm and the recipient’s public key. The result is a ciphertext message, which is sent to the recipient. The recipient then decrypts this message back as plaintext, by using the private key corresponding to the public key the sender used to encrypt the message.

Compared to asymmetric cryptography, symmetric cryptography is much simpler, as the same key is shared between sender and receiver. Asymmetric encryption needs more processing resources to encrypt a message then asymmetrically encrypt the shared key. However, asymmetric encryption offers a number of advantages over symmetric encryption, including:

  • Simplified key distribution
  • Digital signature
  • Long-term encryption

Strong Encryption

Strong encryption refers to ciphers that are virtually unbreakable without the decryption keys. This method of encryption relies on a very large number (256 bits) as a cryptographic key. However, the practice of strong encryption is controversial. While most companies and consumers believe it is a security measure, governments tend to view strong encryption as a potential means by which criminal activity or harassment could be concealed. The concern is that stalkers, predators or terrorists could disguise their identities through encryption, essentially becoming untraceable to authorities.

Certain governments, including that of the United States, are pushing for key escrow systems for strong encryption. Key escrow systems involve a trusted third party, who holds the encryption key on behalf of the government. This third party may be a bank or new federal office created by Congress. Everyone who uses a strong encryption would essentially be required to provide the government with a copy of the key. Decryption keys would then be stored securely and only used by authorities with the appropriate court orders. A significant concern about the key escrow system is that the keys are held in a single, central location, which would present a risk for hacker attacks. It is possible for criminals to hack into the key database and steal or modify the keys.

Summary

This article discusses cryptography, the practice of encrypting and decrypting data in order to ensure confidentiality and integrity. The article explores various levels of encryption, including field-level, file-level and full-drive encryption. It also explores cryptography in relation to associated concepts, such as authentication, confidentiality, integrity and non-repudiation. The article then compares two types of encryption schemes: symmetric encryption (also called private key encryption) and asymmetric encryption (also called public key encryption). Finally, it discusses the controversy surrounding strong encryption, which may inadvertently disguise criminal activity.

Foundations Exam Preparation

In preparation for the Foundations exam, a privacy professional should be comfortable with topics related to this post, including:

  • Cryptography (II.C.a.iii.)
  • Digital signatures (II.C.b.vi.5.)
  • Non-repudiation (II.C.b.vi.6.)
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