A block cipher algorithm designed by the National Security Agency as part of the Capstone chip used in the Fortezza PCMCIA cards, the Clipper chip, and also for the Defense Messaging System. In the taxonomy of ciphers it is an unbalanced Feistel network with a block size of 64 bits, an 80-bit key, and 32 rounds. The key escrow features the Clipper Chip was infamous for are not embodied here, but in the protocol used by the chip. The NSA considers it a "high risk algorithm", meaning they considered it likely that it be reverse engineered, so it's improbable that they used their most clever and secret design methodologies to make it. It was declassified in 1998 and specifications are available from NIST and public domain code implementations are available all over the Internet.

Skipjack is an encryption algorithm, a symmetric block cipher designed by the NSA. It is best known for its part in the infamous Capstone and Clipper key escrow systems pushed by the American government. The algorithm was kept secret by the NSA until June 23, 1998, when problems arose with the Capstone-enabled Fortezza secure communication system. The NSA was forced to abandon tamper-proof hardware, and in doing so, violated its rules for the use of classified algorithms. The cost of declassifying Skipjack must have been less than reworking Fortezza.

The algorithm itself is a 64-bit block cipher, which means it takes 64 bits of information as input, and produces 64 bits of scrambled output. The key is always 80 bits long. It is a hybrid of Feistel network and shift register designs. Despite being part of Capstone and Clipper, Skipjack does not have any key escrow built-in; that aspect of those systems was provided by sending part of the Skipjack key encrypted with a different algorithm. A public key of the escrow agency was used encrypt it, and the carefully guarded private key would be used to recover it, allowing the authorities to recover enough of the Skipjack key to enable a brute force attack.

Although Skipjack has been analyzed far less than other algorithms such as DES due to its relative newness, it is widely believed to be secure. Skipjack was designed primarily as a replacement for DES, an older, widely-used, standard algorithm. It improves on DES in a few areas:

  • the key length is longer (Skipjack uses 80 bits versus 56 bits for DES) making brute force attacks millions of times slower; however 80 bits is still regarded as too short by many
  • DES has some known weaknesses, such as bad keys (a small subset of DES keys produce highly recognizable ciphertext); Skipjack avoids these problems
  • Skipjack is more simple to implement and is about twice as fast as DES on comparable hardware

The algorithm was always intended to be widely deployed in consumer goods employing Capstone and Clipper, so even with tamper-proof hardware the algorithm was likely to be uncovered. There is nothing exceptional in Skipjack, and many speculate that the NSA avoided its most advanced cryptography when designing it.

Rare Commercial Sailboats Still in Use


The skipjack is a working sailboat, a one mast, "two sail bateau" design originated in 1890 on the Eastern Shore of the Chesapeake Bay in Maryland, USA, and is named after a jumping bluefish. It had a jib, mast, and a mainsail. It was economical to build, and even though it developed into a vessel that was thick timbered and therefore sturdily built, these sluggish ladies they later made more relatively quick for their era. It had a shallow "V" hull, and the keel, (vertcal underwater fin) had a centerboard that was lowered into the water giving stability against capsizing in 50 foot plus deep water, could be raised to navigate the 3 foot depths, (so they could emulate the skipjack fish.)

Chesapeake Bay Moving Landmark

They are the last of this kind making a living while wafting canvas propels them from one oyster bed to another for the winter (the season starts in October) "drudgin'", that is, harvesting oysters by dredging off the floor -- but originally they were the main source of all Chesapeake transport and commerce of agricultural goods. Most were manufactured on Deal Island, which is on Maryland's Eastern Shore, Wicomico County and is the site of the annual Labor Day Skipjack Races and Land Festival. By the turn of the century there were around a thousand skipjacks, now only 10 work of the 20 remaining. You can see them on any day moored in the little harbor at Wenona.

Pearl of Great Price

The last one made was the City of Crisfield in 1955 (a racing champion as well), and by 1957 there still were 80 boats harvesting the world's largest estuary's bounty. Since then the loss of 60 of those boats has outpaced the constant striving for their restoration. The oyster has been decimated by pollution, therefore the future of the working class sailboat is in question. Since yawls are only allowed by law to use motors on Mondays, (later Tuesdays, too) the rest of the dredging was left the rest of the week to the practicality of moving air on cloth. One percent of the oyster harvest is made by these usuable relics.

It's the Law!

In Chapter 788, Acts of 1985; Code State Government Article, section 13-312 Maryland made the skipjack the official State Boat.


The Chesapeake Bay magazine online
State of Maryland Archives online
Ellen Wilson JBHS

Skip"jack` (?), n.


An upstart.



2. Zool.

An elater; a snap bug, or snapping beetle.

3. Zool.

A name given to several kinds of a fish, as the common bluefish, the alewife, the bonito, the butterfish, the cutlass fish, the jurel, the leather jacket, the runner, the saurel, the saury, the threadfish, etc.

4. Naut.

A shallow sailboat with a rectilinear or V-shaped cross section.


© Webster 1913.

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