S Salt, Sample, S-Box, Scalable, Secrecy, Secret Code, Secret Key Cipher, Security, Security Through Obscurity, Semiconductor, Semigroup, Session Key, Set, Shift Register, Shuffle, Sieve of Eratosthenes, Significance, Simple Substitution, Software, Source Code, State, Stationary Process, Statistic, Statistics, Steganography, Stochastic, Stream Cipher, Strength, Strict Avalanche Criterion (SAC), Subjective, Substitution, Substitution- Permutation, Substitution Table, Superencryption, Surjective, Switch, Switching Function, Symmetric Cipher, Symmetric Group, System, System Design T Table Selection Combiner, TEMPEST, Transformer, Transistor, Transposition, Trap Door, Triple DES, Truly Random, Trust, Truth Table, Type I Error, Type II Error U Unary, Unexpected Distance, Unicity Distance, Uniform Distribution V Variable Size Block Cipher, Voltage W Walsh Functions, Weight, Whitening White Noise Wire X XOR Absolute In the study of logic, something observed similarly by most observers, or something agreed upon, or which has the same value each time measured. Something not in dispute, unarguable, and independent of other state. As opposed to contextual. AC Alternating Current: Electrical power which repeatedly reverses direction of flow. As opposed to DC. Generally used for power distribution because the changing current supports the use of transformers. Utilities can thus transport power at high voltage and low current, which minimize "ohmic" or I 2 R losses. The high voltages are then reduced at power substations and again by pole transformers for delivery to the consumer. Additive Combiner An additive combiner uses numerical concepts similar to addition to mix multiple values into a single result. One example is byte addition modulo 256, which simply adds two byte values, each in the range 0 255, and produces the remainder after division by 256, again a value in the byte range of 0 255. Subtraction is also an "additive" combiner. Another example is bit-level exclusive-OR which is addition mod 2. A byte- level exclusive-OR is a polynomial addition. Additive RNG (Additive random number generator.) A LFSR-based RNG typically using multi-bit elements and integer addition (instead of XOR) combining. References include: Knuth, D. 1981. The Art of Computer Programming, Vol. 2, Seminumerical Algorithms. 2nd ed. 26-31. Addison-Wesley: Reading, Massachusetts. Marsaglia, G. and L. Tsay. 1985. Matrices and the Structure of Random Number Sequences. Linear Algebra and its Applications. 67: 147-156. Advantages include: A long, mathematically proven cycle length. Especially efficient software implementations. Almost arbitrary initialization (some element must have its least significant bit set). A simple design which is easy to get right. In addition, a vast multiplicity of independent cycles has the potential of confusing even a "quantum computer," should such a thing become possible. For Degree-n Primitive, and Bit Width w Total States: 2 nw Non-Init States: 2 n(w-1) Number of Cycles: 2 (n-1)(w-1) Length Each Cycle: (2 n -1)2 (w-1) Period of LSB: 2 n -1 The binary addition of two bits with no carry input is just XOR, so the lsb of an Additive RNG has the usual maximal length period. A degree-127 Additive RNG using 127 elements of 32 bits each has 2 4064 unique states. Of these, 2 3937 are disallowed by initialization (the lsb's are all "0") but this is just one unusable state out of 2 127 . There are still 2 3906 cycles which each have almost 2 158 steps. (The Cloak2 stream cipher uses an Additive RNG with 9689 elements of 32 bits, and so has 2 310048 unique states. These are mainly distributed among 2 300328 different cycles with almost 2 9720 steps each.) Note that any LFSR, including the Additive RNG, is very weak when used alone. But when steps are taken to hide the sequence (such as using a jitterizer and Dynamic Substitution combining) the result can have significant strength. Affine Generally speaking, linear. Sometimes affine generalizes "linearity" to expressions of multiple independent variables, with only a single-variable expression being called "linear." From analytic and algebraic geometry. Assume the flat plane defined by two arbitrary unit vectors e 1 , e 2 and a common origin O; this is a coordinate "frame." Assume a grid of lines parallel to each frame vector, separated by unit lengths (a "metric" which may differ for each vector). If the vectors happen to be perpendicular, we have a Cartesian coordinate system, but in any case we can locate any point on the plane by its position on the grid. An affine transformation can change the origin, the angle between the vectors, and unit vector lengths. Shapes in the original frame thus become "pinched," "squashed" or "stretched" images under the affine transformation. This same sort of thing generalizes to higher degree expressions. The Handbook of Mathematics says that if e 1 , e 2 , e 3 are linearly independent vectors, any vector a can be expressed uniquely in the form a = a 1 e 1 + a 2 e 2 + a 3 e 3 where the a i are the affine coordinates. (p.518) The VNR Concise Encyclopedia of Mathematics says "All transformations that lead to a uniquely soluble system of linear equations are called affine transformations." (p.534) Affine Boolean Function A Boolean function which can be represented in the form: a n x n + a n-1 x n-1 + + a 1 x 1 + a 0 where the operations are mod 2: addition is Exclusive-OR, and multiplication is AND. Note that all of the variables x i are to the first power only, and each coefficient a i simply enables or disables its associated variable. The result is a single Boolean value, but the constant term a 0 can produce either possible output polarity. Here are all possible 3-variable affine Boolean functions (each of which may be inverted by complementing the constant term): affine truth table c 0 0 0 0 0 0 0 0 x0 0 1 0 1 0 1 0 1 x1 0 0 1 1 0 0 1 1 x1+x0 0 1 1 0 0 1 1 0 x2 0 0 0 0 1 1 1 1 x2+ x0 0 1 0 1 1 0 1 0 x2+x1 0 0 1 1 1 1 0 0 x2+x1+x0 0 1 1 0 1 0 0 1 Alphabet The set of symbols under discussion. Alternative Hypothesis In statistics, the statement formulated so that the logically contrary statement, the null hypothesis H 0 has a test statistic with a known distribution for the case when there is nothing unusual to detect. Also called the research hypothesis H 1 , and logically identical to "NOT-H 0 " or "H 0 is not true." Amplifier a component or device intended to sense a signal and produce a larger version of that signal. In general, any amplifying device is limited by available power, frequency response, and device maximums for voltage, current, and power dissipation. Transistors are analog amplifiers which are basically linear over a reasonable range and so require DC power. In contrast, Relays are classically mechanical devices with direct metal-to-metal moving connections, and so can handle generally higher power and AC current. Amplitude The signal level, or height. Analog Pertaining to continuous values. As opposed to digital or discrete quantities. AND A Boolean logic function which is also mod 2 multiplication. ASCII A public code for converting between 7-bit values 0 127 (or 00 7f hex) and text characters. ASCII is an acronym for American Standard Code for Information Interchange. DEC HEX CTRL CMD DEC HEX CHAR DEC HEX CHAR DEC HEX CHAR 0 00 ^@ NUL 32 20 SPC 64 40 @ 96 60 ' 1 01 ^A SOH 33 21 ! 65 41 A 97 61 a 2 02 ^B STX 34 22 " 66 42 B 98 62 b 3 03 ^C ETX 35 23 # 67 43 C 99 63 c 4 04 ^D EOT 36 24 $ 68 44 D 100 64 d 5 05 ^E ENQ 37 25 % 69 45 E 101 65 e 6 06 ^F ACK 38 26 & 70 46 F 102 66 f 7 07 ^G BEL 39 27 ' 71 47 G 103 67 g 8 08 ^H BS 40 28 ( 72 48 H 104 68 h 9 09 ^I HT 41 29 ) 73 49 I 105 69 i 10 0a ^J LF 42 2a * 74 4a J 106 6a j 11 0b ^K VT 43 2b + 75 4b K 107 6b k 12 0c ^L FF 44 2c , 76 4c L 108 6c l 13 0d ^M CR 45 2d - 77 4d M 109 6d m 14 0e ^N SO 46 2e . 78 4e N 110 6e n 15 0f ^O SI 47 2f / 79 4f O 111 6f o 16 10 ^P DLE 48 30 0 80 50 P 112 70 p 17 11 ^Q DC1 49 31 1 81 51 Q 113 71 q 18 12 ^R DC2 50 32 2 82 52 R 114 72 r 19 13 ^S DC3 51 33 3 83 53 S 115 73 s 20 14 ^T DC4 52 34 4 84 54 T 116 74 t 21 15 ^U NAK 53 35 5 85 55 U 117 75 u