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Movements, leaders, victories and the continuing fight for equality.
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Meet the people whose lives, choices and achievements shaped the journey.
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Katherine Johnson’s mathematical calculations helped guide some of America’s most important early space missions while she confronted the racial and gender barriers faced by Black women in twentieth-century America.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
Locks-and-keys is a solution to dangling pointers in computer programming languages. The locks-and-keys approach represents pointers as ordered pairs (key, address) where the key is an integer value. Heap-dynamic variables are represented as the storage for the variable plus a cell for an integer lock value. When a variable is allocated, a lock value is created and placed both into the variable's cell and into the pointer's key cell. Every access to the pointer compares these two values, and access is allowed only if the values match. When a variable is deallocated, the key of its pointer is modified to hold a value different from the variable's cell. From then on, any attempt to dereference the pointer can be flagged as an error. Since copying a pointer also copies its cell value, changing the key of the ordered pair safely disables all copies of the pointer.
A car key or an automobile key is a key used to open and/or start an automobile. Modern key designs are usually symmetrical, and some use grooves on both sides, rather than a cut edge, to actuate the lock. It has multiple uses for the automobile with which it was sold. A car key can open the doors, as well as start the ignition, open the glove compartment and also open the trunk (boot) of the car. Some cars come with an additional key known as a valet key that starts the ignition and opens the driver's side door, but prevents the valet from gaining access to valuables that are located in the trunk or the glove box. Some valet keys, particularly those to high-performance vehicles, go so far as to restrict the engine's power output to prevent joyriding. Recently, features such as coded immobilizers have been implemented in newer vehicles. More sophisticated systems make ignition dependent on electronic device, rather than the mechanical keyswitch. A number of these systems, such as KeeLoq and Megamos Crypto have been demonstrated to be weak and vulnerable to cryptanalytic attacks. Ignition switches or locks are combined with security locking of the steering column (in many modern vehicles) or the gear lever (such as in Saab Automobile vehicles). In the latter, the switch is between the seats, preventing damage to the driver's knee in the event of a collision. Keyless entry systems, which use a door-mounted keypad, key fob, a wireless-enabled handheld computing device (e.g., smartphone or tablet), or a remote control in place of a toothed key, have become a standard feature on most new cars. Some of them are handsfree in that a vehicle door is automatically unlocked when the user's handheld device is detected within proximity to the vehicle. Some high-tech automotive keys are billed as theft deterrents. Mercedes-Benz uses a key that, rather than have a cut metal piece to start the car, uses an encoded infrared beam that communicates with the car's computer. If the codes match, the car can be started. These keys can be expensive to replace if lost and can cost up to US $400. A switchblade key is basically the same as any other car key, except in appearance. The switchblade key is designed to fold away inside the fob when it is not being used. Switchblade keys have become very popular recently because of their smart compact look. These types of keys are also commonly referred to as "flip keys." Because switchblade keys are only developed for new car models, they are usually equipped with a programmed transponder chip.
This glossary lists types of keys as the term is used in cryptography, as opposed to door locks. Terms that are primarily used by the U.S. National Security Agency are marked (NSA). For classification of keys according to their usage see cryptographic key types. 40-bit key - key with a length of 40 bits, once the upper limit of what could be exported from the U.S. and other countries without a license. Considered very insecure. See key size for a discussion of this and other lengths. Authentication key - Key used in a keyed-hash message authentication code, or HMAC. Benign key - (NSA) a key that has been protected by encryption or other means so that it can be distributed without fear of its being stolen. Also called BLACK key. Content-encryption key (CEK) a key that may be further encrypted using a KEK, where the content may be a message, audio, image, video, executable code, etc. Crypto ignition key An NSA key storage device (KSD-64) shaped to look like an ordinary physical key. Cryptovariable - NSA calls the output of a stream cipher a key or key stream. It often uses the term cryptovariable for the bits that control the stream cipher, what the public cryptographic community calls a key. Data encryption key (DEK) used to encrypt the underlying data. Derived key - keys computed by applying a predetermined hash algorithm or key derivation function to a password or, better, a passphrase. DRM key - A key used in digital rights management to protect media Electronic key - (NSA) key that is distributed in electronic (as opposed to paper) form. See EKMS. Ephemeral key - A key that only exists within the lifetime of a communication session. Expired key - Key that was issued for a use in a limited time frame (cryptoperiod in NSA parlance) which has passed and, hence, the key is no longer valid. FIREFLY key - (NSA) keys used in an NSA system based on public key cryptography. Key derivation function (KDF) - function used to derive a key from a secret value, e.g. to derive KEK from Diffie-Hellman key exchange. Key encryption key (KEK) - key used to protect MEK keys (or DEK/TEK if MEK is not used). Key production key (KPK) -Key used to initialize a keystream generator for the production of other electronically generated keys. Key fill - (NSA) loading keys into a cryptographic device. See fill device. Master key - key from which all other keys (or a large group of keys) can be derived. Analogous to a physical key that can open all the doors in a building. Master encryption key (MEK) - Used to encrypt the DEK/TEK key. Master key encryption key (MKEK) - Used to encrypt multiple KEK keys. For example, an HSM can generate several KEK and wrap them with an MKEK before export to an external DB - such as OpenStack Barbican. One time pad (OTP or OTPad) - keying material that should be as long as the plaintext and should only be used once. If truly random and not reused it's the most secure encryption method. See one-time pad article. One time password (OTP) - One time password based on a prebuilt single use code list or based on a mathematical formula with a secret seed known to both parties, uses event or time to modify output (see TOTP/HOTP). Paper key - (NSA) keys that are distributed in paper form, such as printed lists of settings for rotor machines, or keys in punched card or paper tape formats. Paper keys are easily copied. See Walker spy ring, RED key. Poem key - Keys used by OSS agents in World War II in the form of a poem that was easy to remember. See Leo Marks. Public/private key - in public key cryptography, separate keys are used to encrypt and decrypt a message. The encryption key (public key) need not be kept secret and can be published. The decryption or private key must be kept secret to maintain confidentiality. Public keys are often distributed in a signed public key certificate. Public key infrastructure - (PKI) a set of roles, policies, hardware, software and procedures needed to create, manage, distribute, use, store and revoke digital certificates and manage public-key encryption. Pre-placed key - (NSA) large numbers of keys (perhaps a year's supply) that are loaded into an encryption device allowing frequent key change without refill. RED key - (NSA) symmetric key in a format that can be easily copied, e.g. paper key or unencrypted electronic key. Opposite of BLACK or benign key. Revoked key - a public key that should no longer be used, typically because its owner is no longer in the role for which it was issued or because it may have been compromised. Such keys are placed on a certificate revocation list or CRL. Session key - key used for one message or an entire communications session. See traffic encryption key. Symmetric key - a key that is used both to encrypt and decrypt a message. Symmetric keys are typically used with a cipher and must be kept secret to maintain confidentiality. Traffic encryption key (TEK)/data encryption key (DEK) - a symmetric key that is used to encrypt messages. TEKs are typically changed frequently, in some systems daily and in others for every message. See session key. DEK is used to specify any data form type (in communication payloads or anywhere else). Transmission security key (TSK) - (NSA) seed for a pseudorandom number generator that is used to control a radio in frequency hopping or direct-sequence spread spectrum modes. See HAVE QUICK, SINCGARS, electronic warfare. Seed key - (NSA) a key used to initialize a cryptographic device so it can accept operational keys using benign transfer techniques. Also a key used to initialize a pseudorandom number generator to generate other keys. Signature key - public key cryptography can also be used to electronically sign messages. The private key is used to create the electronic signature, the public key is used to verify the signature. Separate public/private key pairs must be used for signing and encryption. The former is called signature keys. Stream key - the output of a stream cipher as opposed to the key (or cryptovariable in NSA parlance) that controls the cipher Training key - (NSA) unclassified key used for instruction and practice exercises. Type 1 key - (NSA) keys used to protect classified information. See Type 1 product. Type 2 key - (NSA) keys used to protect sensitive but unclassified (SBU) information. See Type 2 product. Vernam key - Type of key invented by Gilbert Vernam in 1918. See stream key. Zeroized key - key that has been erased (see zeroisation.)
A concurrent hash table or concurrent hash map is an implementation of hash tables allowing concurrent access by multiple threads using a hash function. Concurrent hash tables represent a key concurrent data structure for use in concurrent computing which allow multiple threads to more efficiently cooperate for a computation among shared data. Due to the natural problems associated with concurrent access - namely contention - the way and scope in which the table can be concurrently accessed differs depending on the implementation. Furthermore, the resulting speed up might not be linear with the amount of threads used as contention needs to be resolved, producing processing overhead. There exist multiple solutions to mitigate the effects of contention, that each preserve the correctness of operations on the table. As with their sequential counterpart, concurrent hash tables can be generalized and extended to fit broader applications, such as allowing more complex data types to be used for keys and values. These generalizations can however negatively impact performance and should thus be chosen in accordance to the requirements of the application.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →Brown v. Board of Education in 1954.
