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Table of contents

Usually, PRNGs are initialized with unpredictable data, called seed data. Seed data may be supplied by a user, generated automatically from the state of the computer, or obtained from a hardware true random number generator.

Cryptographically strong PRNGs use cryptographic functions. Along with good seed data, they produce unpredictable and statistically random numbers.

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On the cryptographic coprocessor, an electronic noise source provides unpredictable input to a random bit-value accumulator. Periodically, the hardware outputs seed to a FIPS approved pseudorandom number generator. The FIPS algorithm is seeded from a system seed digest. System-generated seed can never be truly unpredictable. If a cryptographic coprocessor is not available, you should add your own random seed via the Add Seed for Pseudorandom Number Generator API to the system seed digest.

This should be done as soon as possible any time the Licensed Internal Code is installed. We can roughly categorize cryptographic operations into five groups: data confidentiality, authentication including data integrity and non-repudiation , random number generation, financial PINs, and key management. Algorithms, operations, and System i implementations 19 2.

The following operations are included in data confidentiality.

Specializations

Encrypt and decrypt The encrypt operation changes plaintext data into ciphertext through the use of a cipher algorithm and key. To restore the plaintext data, the decrypt operation must employ the same algorithm and key. Encryption and decryption may be employed at any level of the operating system. The application may or may not be aware that encryption is happening. The user application completely controls key generation, selection, distribution, and what data to encrypt.

Note: This book deals with field level encryption. Translate The translate operation decrypts data from encryption under one key and encrypts the data under another key. This is done in one step to avoid exposing the plaintext data within the application program. To rely on data, you need to know that it comes from an authorized source and is unchanged.

Additional cryptographic operations are required for these purposes. Hash or message digest Hash operations are useful for authentication purposes.

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For example, you can keep a copy of a digest for the purpose of comparing it with a newly generated digest at a later date. If the digests are identical, the data has not been altered. The input data is encrypted using CBC mode. But instead of returning the entire ciphertext, it returns the last block of encrypted data.

This value is called a MAC and is used to ensure that the data has not been modified. Typically, a MAC is appended to the end of a message. You must use the MAC operation and then encrypt the entire message to ensure both data privacy and integrity. It is used in the same way in which a MAC is used.

A sign operation works as follows: 1. The data to be signed is hashed to produce a digest. The verify operation works as follows: 1. The signature is decrypted using the sender's PKA public key to produce digest 1. If the two digests are equal, the signature is valid. Theoretically, this also verifies the sender because only the sender should posses the private key. However, how can the receiver verify that the public key actually belongs to the sender?

Certificates are used to help solve this problem. An important use of random numbers is in the generation of cryptographic key material. Key generation has been described as the most sensitive of all computer security functions. If the random numbers are not cryptographically strong, the function will be subject to attack. A PIN is a unique number assigned to an individual by an organization. PINs are commonly assigned to customers by financial institutions. The PIN is typed in at a keypad and compared with other customer-associated data to provide proof of identity.

Other processing is done on the PIN as well, such as putting it in a particular format. The cryptographic coprocessors provide a complete set of financial PIN operations. Cryptographic Services does not support any type of PIN operation. Algorithms, operations, and System i implementations 21 2. This includes key storage and retrieval, key encryption and conversions, and key distribution.

A CSP is the software or hardware that implements a set of cryptographic algorithms and operations. IBM Cryptographic Coprocessor is no longer available, but is still supported. The Cryptographic Accelerator was designed to improve the performance of SSL for those applications that do not require hardware-secured key storage. These algorithms are used by many system functions and are available for application use through the Cryptographic Services API set.

Although this book only discusses the first three options, JCE is included for completeness. The CCA and cryptographic coprocessors are used by System i for a number of purposes: — By applications for general-purpose cryptographic operations. Algorithms, operations, and System i implementations 23 Table indicates what CSP is used under each interface. Key management concepts How secure is your encrypted data? It depends on the security of your keys. The security of your keys depends on many factors, such as how you generate keys, store keys, authorize keys, distribute keys, and destroy keys.

All cryptographic algorithms, at least the reputable ones, are in the public domain. Therefore, it is the key that controls access to the data.

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We cannot emphasize enough that you must safeguard the key to protect the data. Therefore, the larger you make your key size, the more prohibitive the search becomes. We discuss key size, or the strength of keys, in terms of number of bits.

However, on some interfaces you may be required to specify the key size in bytes, not bits. For example, to specify a bit key size, you may be required to specify 32 bytes. Deciding on a key size is an important decision. While a larger key size better protects the data, it can also decrease performance.

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Some algorithms only support a few key sizes. Others support a large range of key sizes. DES keys are always 8 bytes in length. So why is the key size not 64? One bit of each byte is sometimes used for parity and is not actually involved in the encryption algorithm. Therefore, the strength of the key is actually Key size must be a multiple of 8. The key size must be an even number. The key size must be a multiple of By security level, we mean the number of steps that it takes to mount a successful attack.

For example, in the case of an exhaustive search on a bit value, the number of steps is two All your cryptographic operations should be designed to meet the security level that you establish. It does not make sense to encrypt data using a bit key, and then encrypt the data-encrypting key under a bit key. Because many encryption modes are susceptible to collision attacks, for a security level of n bits, you should use a key at least 2n bits. For example, for bit security, you should use a bit key.

This is an important consideration because the capabilities for exhaustive attacks in the future will be significantly better than today. If you plan to encrypt and store data for a long period of time without translating at a future date you need to choose a large key size. Cryptographic experts argue that systems today should aim at securing data for 30 to 50 years. That requires designing a system with a bit security level. Comparing the strength of keys can be tricky. In fact, you cannot always compare number of bits between various PKA algorithms.

The security of the algorithm depends on the difficulty of factoring the modulus. Consequently, increasing the modulus size increases the security, but it also becomes much more CPU intensive. The performance for large RSA keys is prohibitive. Until then, you should use at least a 2,bit PKA key size.

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For example, you should not use words for a key value. A program can quickly do an exhaustive search of all words in a dictionary. Using words for a key value provides very little unpredictable data, or entropy. Sometimes words are used to set a key by entering a password or passphrase that is then hashed to the appropriate key size by the system such as with the Set Encryption Password SQL function. In these situations, a large amount of character data must be entered to obtain good entropy.

A good rule of thumb is to assume that your passphrase is only providing 1—2 bits of entropy per byte. So, for example, if you plan to use a bit key you want bits of entropy, and therefore it would be best to enter a passphrase containing characters.