"What if the order were reversed?" asked Samos.
"Doubtless, if that combination were used, it would correlate with a different character," said Bosk.
"We do not have the key to the cipher," said Iskander.
"We can try all combinations!" cried Samos, pounding the table.
"We may suppose," said Bosk, "as a working hypothesis, that the message is in Gorean. As far as we know, Belisarius, whom we know only by name, and it may be a code name, is Gorean."
"Yes?" said Samos.
"See," said Bosk, who was examining the necklace, "the most frequent combination of colors is blue and red."
"So?" asked Samos.
"In Gorean," said Bosk, "the most frequently occurring letter is Eta. We might then begin by supposing that the combination of blue and red signifies an Eta."
"I see," said Samos.
"The next most frequently occurring letters in Gorean," said Bosk, "are Tau, AI-Ka, Omnion and Nu. Following these in frequency of occurrence are Ar, Ina, Shu and Homan, and so on."
"How is this known?" asked Samos.
"It is based upon letter counts," said Bosk, "over thousands of words in varieties of manuscripts."
"These matters have been determined by scribes?" asked Samos.
"Yes," said Bosk.
"Why should they be interested in such things?"
"Such studies were conducted originally, at least publicly, as opposed to the presumed secret studies of cryptographers, in connection with the Sardar Fairs," said Bosk, "at meetings of Scribes concerned to standardize and simplify the cursive alphabet. Also, it was thought to have consequences for improved pedagogy, in teaching children to first recognize the most commonly occurring letters."
"I was taught the alphabet beginning with Al-Ka," smiled Samos.
"As was I," said Bosk. "Perhaps we should first have been taught Eta."
"That is not the tradition!" said Samos.
"True," admitted Bosk. "And these innovative scribes have had little success with their proposed reforms. Yet, from their labors, various interesting facts have emerged. For example, we have learned not only the order of frequency of occurrence of letters but, as would be expected, rough percentages of occurrence as well. Eta, for example, occurs two hundred times more frequently in the language than Altron. Over forty percent of the language consists of the first five letters I mentioned, Eta, Tau, Al-Ka, Omnion and Nu."
"That seems impossible," said Samos.
"It is true," said Bosk. "Further, over sixty percent of the language consists of those five letters plus Ar, Ina, Shu and Homan."
"We could still try all possible combinations," said Samos.
"True," said Bosk, "and, in a short message, which this appears to be, we might produce several intelligible possibilities. Short messages, particularly those which do not reflect statistical letter frequencies, can be extremely difficult to decipher, even when the cipher used is rudimentary."
"Rudimentary?" asked Samos.
"There are many varieties of cipher," said Bosk, "both of the substitution and transposition type. I suspect we have before us, in this necklace, a simple substitution cipher."
"Why?" asked Samos.
"It was interpreted almost instantly by the man called Belisarius," said Bosk. "A more complicated cipher, indexed to key words or key numbers, would presumably have required a wheel or table for its interpretation."
"Can all codes be broken?" asked Samos.
"Do not confuse a code with a cipher," said Bosk. "In a code, a given character, or set of characters, will commonly correlate with a word, as opposed to a letter. Codes require code books. Codes, in effect, cannot be broken. If the code book can be captured, of course, the code is useless. Codes are vulnerable in one way, ciphers in another."
"Do you feel the enemy would risk a code book, or code device, on Gor?" asked Samos.
Bosk smiled. "It seems unlikely," he said.
"Are there Unbreakable ciphers?" asked Samos.
"Yes," said Bosk, "both from a practical and theoretical point of view. From the practical point of view, if a cipher is used briefly and for a given short message, it may be impossible to break. There is just not enough material to work with. From the theoretical point of view, the unique-sequence cipher cannot be broken. It utilizes key words or numbers, but each message is further altered in a prearranged, random manner. Each message is thus unique, but decipherable in its position in the sequence of messages.
Both sender and receiver know, for example, that message six will be randomized in manner six, and so on."
"This is complex," said Samos.
"It requires that both sender and receiver have the deciphering tables at hand," said Bosk. "Thus, although it is more convenient than a code book, it shares some of the vulnerability of the code book."
Samos looked down at the necklace on the table before him. "Why should this be a simple substitution cipher?" he asked.
"I think that it is," said Bosk. "from the ease with which Belisarius read the message. I find it not implausible that it should be a simple substitution cipher because of the simplicity and convenience of such a cipher."
"Is it as secure?" asked Samos.
"The security of this cipher," smiled Bosk, "lies not in itself, as a cipher, but rather, as is common, that it is not understood as a cipher. It is not, for example, a strange message written upon a scrap of paper, calling attention to itself as a secret communication, challenging the curious to its unraveling, but apparently only an innocent necklace, beaded with wood, common, vulgar and cheap, fit only for the throat of a lowly female slave."
Samos lifted the necklace. I did not know what secret it contained.
"Further," said he who was called Bosk of Port Kar, "the slave herself did not understand the nature of her role in these matters. She did not, for a long time, even understand that she bore the message. Great security was achieved, too, in the manner of releasing the behavior of stringing the beads and in the counter-suggestion that she be unable to recall the order of the beads without the appropriate trigger structure being reconstructed." Bosk smiled. "Add to this," said he, "the convenience of a simple substitution cipher, the absence of the necessity for a code book, the lack of need for cipher wheels or deciphering tables, and you have an arrangement of circumstances which maximizes not only security but, under the appropriate conditions, ease of communication."
"Worthy of the enemy," said Samos.
"I think so," said Bosk.
"Could we not seize this Belisarius?" asked Samos.
"We do not know where he is," said Bosk. He looked at Iskander, of the Physicians. "If we should be able to seize him who is spoken of as Belisarius, do you think we could derive the cipher key from him?"
"Perhaps," said Iskander, "but I suspect that a spoken word, uttered by Belisarius himself, would, by suggestion, remove the cipher key from his mind."
"Could the enemy be so subtle?" asked Samos.
Iskander, of the Physicians, pointed to me. "I think so," said he. "You see what their power is in such matters."
I looked down.
"Could we, by the use of drugs, obtain it?" asked Samos.
"Perhaps," said Iskander, "but presumably we would encounter numerous keys. Who knows?"
Samos looked at Bosk. "Can you read the cipher?" he asked.
"I do not know," said Bosk. "See the repetitions of the beads. There are several repetitions, to compose the entire necklace. The message itself is thus short."
"It may be impossible to rend?" asked Samos.
"Yes," said Bosk.
Samos looked at me. "I wonder," said he, "why, when finished with this wench, they did not cut her throat?"
I shuddered.
"They apparently feared little," said Bosk. "Their security, they deemed, was impregnable."