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<title>Cryptography concepts</title>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Cryptography concepts</h1>
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<div><p>This article provides a basic understanding of cryptographic function
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and an overview of the server's cryptographic services</p>
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<div class="section"><h4 class="sectiontitle">Cryptography</h4><p>Cryptographic services help ensure
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data privacy, maintain data integrity, authenticate communicating parties,
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and prevent repudiation (when a party refutes having sent a message).</p>
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<p>Basic
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encryption allows you to store information or to communicate with other parties
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while preventing non-involved parties from understanding the stored information
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or understanding the communication. Encryption transforms understandable text
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(plaintext) into an unintelligible piece of data (ciphertext). Decryption
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restores the understandable text from the unintelligible data. Both functions
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involve a mathematical formula (the algorithm) and secret data (the key).</p>
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</div>
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<div class="section"><h4 class="sectiontitle">Cryptographic algorithms</h4><p>There are two types of
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cryptographic algorithms:</p>
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<ol><li>With a <dfn class="term">secret</dfn> or <dfn class="term">symmetric</dfn> key algorithm, the
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key is a shared secret between two communicating parties. Encryption and decryption
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both use the same key. The Data Encryption Standard (DES) and the Advanced
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Encryption Standard (AES) are examples of symmetric key algorithms. <div class="p">There
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are two types of symmetric key algorithms: <dl><dt class="dlterm">Block ciphers</dt>
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<dd>In a block cipher, the actual encryption code works on a fixed-size block
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of data. Normally, the user's interface to the encrypt/decrypt operation will
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handle data longer than the block size by repeatedly calling the low-level
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encryption function. If the length of data is not on a block size boundary,
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it must be padded.</dd>
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<dt class="dlterm">Stream ciphers</dt>
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<dd>Stream ciphers do not work on a block basis, but convert 1 bit (or 1 byte)
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of data at a time.</dd>
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</dl>
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</div>
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</li>
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<li>With a <dfn class="term">public key</dfn> (PKA) or <dfn class="term">asymmetric key</dfn> algorithm,
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a pair of keys is used. One of the keys, the private key, is kept secret and
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not shared with anyone. The other key, the public key, is not secret and can
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be shared with anyone. When data is encrypted by one of the keys, it can only
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be decrypted and recovered by using the other key. The two keys are mathematically
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related, but it is virtually impossible to derive the private key from the
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public key. The RSA algorithm is an example of a public key algorithm. <p>Public
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key algorithms are slower than symmetric key algorithms. Applications typically
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use public key algorithms to encrypt symmetric keys (for key distribution)
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and to encrypt hashes (in digital signature generation).</p>
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</li>
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</ol>
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<p>Together, the key and the cryptographic algorithm transform the data.
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All of the supported algorithms are in the public domain. Therefore it is
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the key that controls access to the data. You must safeguard the keys to protect
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the data.</p>
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</div>
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<div class="section"><h4 class="sectiontitle">Cryptographic operations</h4><p>Different cryptographic <em>operations</em> may
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use one or more <em>algorithms</em>. You choose the cryptographic operation
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and algorithm(s) depending on your purpose. For example, for the purpose of
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ensuring data integrity, you might want to use a MAC (message authentication
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code) operation with the AES algorithm.</p>
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<p>The system provides several
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API sets that support cryptographic operations. See the <strong>System cryptography
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overview</strong> information at the bottom of this topic for more information.</p>
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</div>
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<div class="section"><h4 class="sectiontitle">Data privacy</h4><p>Cryptographic operations for the purpose
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of data privacy (confidentiality) prevent an unauthorized person from reading
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a message. The following operations are included in data privacy:</p>
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<dl><dt class="dlterm"><dfn class="term">Encrypt and Decrypt</dfn></dt>
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<dd>The encrypt operation changes plaintext data into ciphertext through the
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use of a cipher algorithm and key. To restore the plaintext data, the decrypt
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operation must employ the same algorithm and key. <div class="p">Encryption and decryption
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may be employed at any level of the operating system. There are three levels: <dl><dt class="dlterm">Field level encryption</dt>
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<dd>With field level encryption, the user application explicitly requests
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cryptographic services. The user application completely controls key generation,
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selection, distribution, and what data to encrypt.</dd>
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<dt class="dlterm">Session level encryption</dt>
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<dd>With encryption at the session layer, the system requests cryptographic
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services instead of an application. The application may or may not be aware
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that encryption is happening.</dd>
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<dt class="dlterm">Link level encryption</dt>
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<dd>Link level encryption is performed at the lowest level of the protocol
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stack, usually by specialized hardware.</dd>
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</dl>
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The Cryptographic Coprocessors and the 2058 Cryptographic Accelerator
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may be used for both field level encryption and Secure Sockets Layer (SSL)
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session establishment encryption. While VPN is supported in i5/OS™, it does
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not use either coprocessor or the accelerator. Furthermore, the system does
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not support SNA session level encryption at all.</div>
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</dd>
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<dt class="dlterm"><dfn class="term">Translate</dfn></dt>
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<dd>The translate operation decrypts data from encryption under one key and
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encrypts the data under another key. This is done in one step to avoid exposing
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the plaintext data within the application program.</dd>
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</dl>
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</div>
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<div class="section"><h4 class="sectiontitle">Data integrity, authenticity, and non-repudiation</h4><p>Encrypted
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data does not mean the data can not be manipulated (e.g. repeated, deleted,
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or even altered). To rely on data, you need to know that it comes from an
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authorized source and is unchanged. Additional cryptographic operations are
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required for these purposes.</p>
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<dl><dt class="dlterm"><dfn class="term">Hash (Message Digest)</dfn></dt>
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<dd>A cryptographic hash operation produces a fixed-length output string (often
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called a digest) from a variable-length input string. For all practical purposes,
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the following statements are true of a good hash function: <ul><li>Collision resistant: If any portion of the data is modified, a different
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hash will be generated.</li>
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<li>One-way: The function is irreversible. That is, given a digest, it is
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not possible to find the data that produces it.</li>
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</ul>
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These properties make hash operations useful for authentication purposes.
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For example, you can keep a copy of a digest for the purpose of comparing
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it with a newly generated digest at a later date. If the digests are identical,
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the data has not been altered.</dd>
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<dt class="dlterm"><dfn class="term">MAC (Message Authentication Code)</dfn></dt>
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<dd>A MAC operation uses a secret key and cipher algorithm to produce a value
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(the MAC) which later can be used to ensure the data has not been modified.
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Typically, a MAC is appended to the end of a transmitted message. The receiver
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of the message uses the same MAC key, and algorithm as the sender to reproduce
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the MAC. If the receiver's MAC matches the MAC sent with the message, the
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data has not been altered. <p>The MAC operation helps authenticate messages,
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but does not prevent unauthorized reading because the transmitted data remains
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as plaintext. You must use the MAC operation and then encrypt the entire message
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to ensure both data privacy and integrity.</p>
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</dd>
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<dt class="dlterm"><dfn class="term">HMAC (Hash MAC)</dfn></dt>
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<dd>An HMAC operation uses a cryptographic hash function and a secret shared
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key to produce an authentication value. It is used in the same way a MAC is
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used.</dd>
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<dt class="dlterm"><dfn class="term">Sign/Verify</dfn></dt>
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<dd>A sign operation produces an authentication value called a digital signature.
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A sign operation works as follows: <ol><li>The data to be signed is hashed, to produce a digest.</li>
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<li>The digest is encrypted using a PKA algorithm and a private key, to produce
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the signature.</li>
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</ol>
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The verify operation works as follows: <ol><li>The signature is decrypted using the sender's PKA public key, to produce
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digest 1. </li>
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<li>The data that was signed is hashed, to produce digest 2.</li>
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<li>If the two digests are equal, the signature is valid.</li>
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</ol>
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Theoretically, this also verifies the sender because only the sender
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should posses the private key. However, how can the receiver verify that the
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public key actually belongs to the sender? Certificates are used to help solve
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this problem.</dd>
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</dl>
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</div>
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<div class="section"><h4 class="sectiontitle">Key and random number generation</h4><p>Many security-related
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functions rely on random number generation, for example, salting a password
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or generating an initialization vector. An important use of random numbers
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is in the generation of cryptographic key material. Key generation has been
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described as the most sensitive of all computer security functions. If the
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random numbers are not cryptographically strong, the function will be subject
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to attack.</p>
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<p>The i5/OS operating system contains a pseudorandom number
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generator (PRNG). The PRNG is used by many system functions and is available
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for application use through the <cite>Cryptographic Services</cite> API set.</p>
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<p>The
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PRNG is composed of two parts: pseudorandom number generation and seed management.
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Pseudorandom number generation is performed using the FIPS 186-1 algorithm.
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Cryptographically strong pseudorandom numbers rely on good seed. The FIPS
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186-1 key and seed values are obtained from a system seed digest. The system
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automatically generates seed using data collected from system information
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or by using the random number generator function on a cryptographic coprocessor
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if one is available. System-generated seed can never be truly unpredictable.
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If a cryptographic coprocessor is not available, you should add your own random
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seed to the system seed digest. This should be done as soon as possible any
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time the Licensed Internal Code is installed.</p>
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</div>
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<div class="section"><h4 class="sectiontitle">Key management</h4><p>Key management is the secure handling
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and storage of cryptographic keys. This includes key storage and retrieval,
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key encryption and conversions, and key distribution.</p>
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<p><strong>Key storage</strong></p>
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<p>Key
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storage on the system includes the following:</p>
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<ul><li>Cryptographic Services key store</li>
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<li>Digital certificate manager certificate store </li>
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<li>CCA key store (used with the Cryptographic Coprocessors) </li>
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<li>JCE key store</li>
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</ul>
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<p>In addition, keys can also be stored on the Cryptographic Coprocessors
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themselves.</p>
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<p><strong>Key Encryption and Conversions</strong></p>
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<div class="p">Keys must be
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encrypted prior to sending or storing them outside the secured system environment.
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In addition, keys should be handled in encrypted form within the system as
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much as possible to reduce the risk of exposure. The management of encrypted
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keys is often done via a hierarchical key system.<ul><li>At the top is a master key (or keys). The master key is the only clear
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key value and must be stored in a secure fashion. </li>
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<li>Key-encrypting keys (KEKs) are used to encrypt other keys. Typically,
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a KEK is used to encrypt a stored key, or a key that is sent to another system.
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KEKs are normally encrypted under a master key. </li>
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<li>Data keys are keys used directly on user data (such as to encrypt or MAC).
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A data key may be encrypted under a KEK or under a master key.</li>
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</ul>
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Various uses of a key will require the key to be in different forms.
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For example, keys received from other sources will normally be converted to
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an internal format. Likewise, keys sent out of the system are converted to
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a standard external format before sending. Certain key forms are standard,
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such as an ASN.1 BER-encoded form, and others are peculiar to a cryptographic
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service provider, such as the Cryptographic Coprocessors.</div>
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<p><strong>Key Distribution</strong></p>
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<div class="p">Typically,
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data encryption is performed using symmetric key algorithms. The symmetric
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keys are distributed using asymmetric key algorithms. Consider these examples:<ul><li><strong>RSA</strong> - An RSA public key is used to encrypt a symmetric key which
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is then distributed. The corresponding private key is used to decrypt it.</li>
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<li><strong>Diffie-Hellman</strong> - The communicating parties generate and exchange
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D-H parameters which are then used to generate key pairs. The public keys
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are exchanged and each party is then able to compute the symmetric key independently.</li>
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</ul>
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</div>
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</div>
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<div class="section"><h4 class="sectiontitle">System cryptography overview</h4><dl><dt class="dlterm">Cryptographic Service Providers</dt>
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<dd>A cryptographic service provider (CSP) is the software or hardware that
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implements a set of cryptographic operations. The system supports several
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CSPs:<ul><li>4758 Cryptographic Coprocessor </li>
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<li>4764 Cryptographic Coprocessor </li>
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<li>2058 Cryptographic Accelerator </li>
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<li>i5/OS LIC
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</li>
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<li>Java™ Cryptography
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Extensions</li>
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</ul>
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</dd>
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<dt class="dlterm">Cryptographic API sets</dt>
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<dd>User applications can utilize cryptographic services indirectly via i5/OS functions
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such as SSL, VPN IPSec, and LDAP. User applications can also access cryptographic
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services directly via the following APIs:<ul><li>CCA<p>The Common Cryptographic Architecture (CCA) API set is provided
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for running cryptographic operations on a Cryptographic Coprocessor. </p>
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</li>
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<li>i5/OS Cryptographic
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Services<p>The i5/OS Cryptographic
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Services API set is provided for running cryptographic operations within the
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Licensed Internal Code or optionally on the 2058 Cryptographic Accelerator. </p>
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</li>
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<li>Java Cryptography<p>Java Cryptography
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Extension (JCE) is a standard extension to the Java Software Development Kit.</p>
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</li>
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<li>Network Authentication Service<p>GSS (Generic Security Services), Java GSS,
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and Kerberos APIs are part of the Network Authentication Service which provides
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authentication and security services. These services include session level
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encryption capability.</p>
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</li>
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<li>i5/OS SSL
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and JSSE<p>i5/OS SSL
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and JSSE support the Secure Sockets Layer Protocol. APIs provide session level
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encryption capability. </p>
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</li>
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<li>SQL<p>Structured Query Language is used to access or modify information
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in a database. SQL supports encryption/decryption of database fields.</p>
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</li>
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</ul>
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</dd>
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</dl>
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This table indicates what CSPs are used under each user interface.
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<div class="tablenoborder"><a name="concepts__cps"><!-- --></a><table cellpadding="4" cellspacing="0" summary="" id="concepts__cps" frame="border" border="1" rules="all"><caption>Table 1. CSPs used under each user interface</caption><thead align="left"><tr valign="bottom"><th align="center" valign="bottom" id="d0e323">CSP APIs</th>
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<th align="center" valign="bottom" id="d0e325">i5/OS LIC</th>
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<th align="center" valign="bottom" id="d0e329">JCE</th>
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<th align="center" valign="bottom" id="d0e331">4764 and 4758</th>
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<th align="center" valign="bottom" id="d0e333">2058</th>
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</tr>
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</thead>
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<tbody><tr><td valign="top" headers="d0e323 "><strong>CCA</strong></td>
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<td align="center" valign="top" headers="d0e325 "> </td>
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<td align="center" valign="top" headers="d0e329 "> </td>
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<td align="center" valign="top" headers="d0e331 ">X</td>
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<td align="center" valign="top" headers="d0e333 "> </td>
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</tr>
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<tr><td valign="top" headers="d0e323 "><strong>i5/OS Cryptographic Services</strong></td>
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<td align="center" valign="top" headers="d0e325 ">X</td>
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<td align="center" valign="top" headers="d0e329 "> </td>
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<td align="center" valign="top" headers="d0e331 "> </td>
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<td align="center" valign="top" headers="d0e333 ">X</td>
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</tr>
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<tr><td valign="top" headers="d0e323 "><strong>Java Cryptography</strong></td>
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<td align="center" valign="top" headers="d0e325 "> </td>
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<td align="center" valign="top" headers="d0e329 ">X</td>
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<td align="center" valign="top" headers="d0e331 "> </td>
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<td align="center" valign="top" headers="d0e333 "> </td>
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</tr>
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<tr><td valign="top" headers="d0e323 "><strong>Network Authentication Service</strong></td>
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<td align="center" valign="top" headers="d0e325 ">X</td>
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<td align="center" valign="top" headers="d0e329 ">X</td>
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<td align="center" valign="top" headers="d0e331 "> </td>
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<td align="center" valign="top" headers="d0e333 "> </td>
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</tr>
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<tr><td valign="top" headers="d0e323 "><strong>i5/OS SSL and JSSE</strong></td>
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<td align="center" valign="top" headers="d0e325 ">X</td>
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<td align="center" valign="top" headers="d0e329 ">X</td>
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<td align="center" valign="top" headers="d0e331 ">X</td>
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<td align="center" valign="top" headers="d0e333 ">X</td>
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</tr>
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<tr><td valign="top" headers="d0e323 "><strong>SQL</strong></td>
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<td align="center" valign="top" headers="d0e325 ">X</td>
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<td align="center" valign="top" headers="d0e329 "> </td>
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<td align="center" valign="top" headers="d0e331 "> </td>
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<td align="center" valign="top" headers="d0e333 "> </td>
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</tr>
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</tbody>
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</table>
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</div>
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</div>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rzajcoverview.htm" title="IBM offers cryptography solutions for customers who require a high level of security.">Cryptography</a></div>
|
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</div>
|
|
<div class="relconcepts"><strong>Related concepts</strong><br />
|
|
<div><a href="rzajcinitialstore.htm" title="A key store file is a database file that stores operational keys, i.e. keys encrypted under the master key. Read this information if you plan to keep records of your DES and PKA keys.">Initialize a key store file</a></div>
|
|
<div><a href="rzajcco4758.htm" title="IBM offers two Cryptographic Coprocessors, which are available on a variety of server models.">4764 and 4758 Cryptographic Coprocessors</a></div>
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|
</div>
|
|
<div class="relinfo"><strong>Related information</strong><br />
|
|
<div><a href="../rzahu/rzahurazhudigitalcertmngmnt.htm">Digital Certificate Manager</a></div>
|
|
<div><a href="../apis/catcrypt.htm">Cryptographic Services API set</a></div>
|
|
<div><a href="../rzahu/rzahurzahu1nmcertstore.htm">Certificate Stores</a></div>
|
|
<div><a href="../rzaha/rzahajce.htm">Java Cryptography Extension</a></div>
|
|
</div>
|
|
</div>
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</body>
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