CRYPTOGRAPHY: THE COMMUNICATION MEANS BETWEEN CUBA AND ITS SPIES
By Manuel Cereijo
The recent captured of more than 12 Cuban spies, including Ana Belen Montes, have shown the way that they communicate with the DGI in Cuba. The basic method is called Cryptography, and Cuba's uses the method developed in the 1970s, referred to as symmetric encryption, secret-key, or single key encryption. There are three important encryption algorithms: DES, triple DES, and AES.
The encryption used by Cuba's intelligence has five ingredients:
· Plaintext: This is the original message or data that is fed into the algorithm as input
· Encryption algorithm: The encryption algorithm performs various substitutions and transformations on the plaintext
· Secret key: The secret key is also input to the algorithm. The exact substitutions and transformations performed by the algorithm depend on the key
· Ciphertext: This is the scrambled message produced as output. It depends on the plaintext and the secret key. For a given message, two different keys will produce two different ciphertexts
· Decryption algorithm: This is essentially the encryption algorithm run in reverse. It takes the ciphertext and the same secret key and produces the original plaintext.
They use two basic important requirements:
· A strong encryption algorithm. They use one that, at the beginning, the opponent who knows the algorithm and has access to one or more ciphertexts, are unable to decipher the ciphertext or figure out the key. It was difficult, at the earlier stages to decipher their messages.
· Sender and receiver (Cuba and the agents here) must have obtained copies of the secret key in a secure fashion and keep the key secure. Once the US intelligence discover the key and knows the algorithm, all communication using this key is readable.
The security of this encryption depends on the secrecy of the key, not the secrecy of the algorithm. That is, they need to keep only the key secret. With the use of this encryption, the principal security problem is maintaining the secrecy of the key.
All their encryption algorithms are based on two general principles: substitution, in which each element in the plaintext (bit, letter, group of bits or letters) is mapped into another element, and transposition, in which elements in the plaintext are rearranged. They use multiple stages of substitutions and transpositions.
Both sender and receiver use the same key. The system is symmetric. A block cipher processes the input one block of elements at a time, producing an output block for each input block. A stream cipher processes the input elements continuously, producing output one element at a time, as it goes along.
The process of attempting to discover the plaintext or key is known as cryptanalysis. A summary follows. The Table summarizes the various types of cryptanalytic attacks or means to decipher Cuba's communication with its spies. The most difficult problem is presented when all that is available is the ciphertext only.
Central to the techniques are the strange laws of quantum mechanics that govern the universe on the smallest scale, and the ability to exploit physics on this scale, which has generated huge interest in Cuba, with the development of a new nanotechnology research and development facilities. The beginning stages of the project were coordinated by Castro Diaz Balart. The quantum properties of photons could make encrypted messages absolutely secure.
It is known that Cuba has experimented already sending encrypted messages through the air over 100 Kms., during days and nights. Cuba expects to be able to send through its Bejucal base these ultra-secret messages by the end of this year or early 2003. Of course, encryption of transmitted data is just one part of keeping information secret. It is easier for a would-be interceptor to compromise other aspects of the overall process that are much more vulnerable than encryption, like hacking the sender's hard drive before the data is encrypted for transmission.
The genius of quantum cryptography is that it solves the problem of key distribution. This ability comes directly from the way quantum particles such as photons behave in nature and the fact that the information these particles carry can take on this behavior. Essentially two technologies make quantum key distribution possible: the equipment for creating photons and that for detecting them. The ideal source is a so-called photon gun that fires a single photon on demand. This is an area where Cuba research and development is highly concentrated and advanced.
The facilities, and the talent, are Cubans. But the financing is from where?
There is work currently going on testing a portable system that can fit in the back of a small trailer and works, on a clear night, over 65 Kms. The cost? Some $90,000. There is work being done on a system that could, on a clear night, beam single photons to orbiting satellites, thereby securing their transmissions. However, where progress has been greatest and where most experimental work has been focused, is on optical-fiber-based communications. ETECSA, the Cuban/Italian telephone company, has just finished the installation of a secret fiber optic ring strictly for military use, around Bejucal, Wajay, Guines, and La Habana. So far the limitation is in the need to use repeaters. The maximum length obtained has been 60 Kms. If distances could be increased, this will be quite a milestone.
Cuba's Bejucal base, which started full operation on January 1998, poses a real threat to the national security of the United States.
Type of attack Known to Cryptanalyst
Ciphertext only Encryption algorithmCiphertext to be decoded
Known plaintext Encryption algorithmCiphertext to be decodedOne or more plaintext-ciphertext pairs formed with the secret key
Chosen plaintext Encryption algorithmCiphertext to be decodedPlaintext message chosen by cryptanalist, together with its corresponding ciphertext generated with the secret key
Chosen ciphertext Encryption algorithm; Ciphertext to be decoded; Purporpoted ciphertext chosen by cryptanalist, together with its corresponding decrypted plaintext generated with the secret key
Chosen Text Encryption algorithm; Ciphertext to be decoded; Plaintext message chosen by cryptanalist, together with its corresponding ciphertext generated with the secret key; Purported ciphertext chosen by cryptanalist, together with its corresponding decrypted plaintext generated with the secret key
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