Cryptographic apparatus and method
First Claim
1. Encryption apparatus for performing symmetric encryption, comprising:
- means (KS) for generating a keystream block (S(i)) in response to an encryption key (K), the keystream block comprising a plurality of bits (s) of a pseudo-random number sequence; and
means (MX) for combining the keystream block (i) with a plaintext block (P(i)) comprising a plurality of bits (b) to produce a ciphertext block (C(i));
wherein the number of bits (s) in the keystream block exceeds the number of bits (b) in the plaintext block.
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Abstract
An encryption system comprises a pseudo-random number generator (KS) for generating a long pseudo-random sequence (S) from a shorter encryption key (K) and, if necessary, a nonce value (N), and a mixing function (MX) for combining the sequence with a plaintext message (P) on a block-by-block basis, where successive blocks (S(i)) of 128 bits of the sequence are combined with successive 64-bit blocks of plaintext (P(i)) to produce successive 64-bit blocks of ciphertext. The blockwise use of a long pseudo-random sequence preserves the advantages of a block cipher in terms of data confidentiality and data integrity, as well as benefiting from the speed advantages of a stream cipher.
133 Citations
29 Claims
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1. Encryption apparatus for performing symmetric encryption, comprising:
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means (KS) for generating a keystream block (S(i)) in response to an encryption key (K), the keystream block comprising a plurality of bits (s) of a pseudo-random number sequence; and means (MX) for combining the keystream block (i) with a plaintext block (P(i)) comprising a plurality of bits (b) to produce a ciphertext block (C(i)); wherein the number of bits (s) in the keystream block exceeds the number of bits (b) in the plaintext block. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 21, 22, 23)
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19. Encryption apparatus comprising:
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a keystream generator (KS) for generating a pseudo-random number sequence in response to an encryption key (K); and processing circuitry (MX) configured to combine a keystream block (S(i)) comprising a bit pattern selected from the pseudo-random number sequence with a plaintext block (P(i)) comprising a bit sequence, said keystream block bit pattern comprising a greater number of bits than the plaintext block bit sequence.
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20. Decryption apparatus for performing symmetric decryption, comprising:
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means (KS) for generating a keystream block (S(i)) in response to a decryption key (K), the keystream block comprising a plurality of bits (s) of a pseudo-random number sequence; and means (MXā
1) for combining the keystream block (S(i)) with a ciphertext block (C(i)) comprising a plurality of bits (b) to recover a plaintext block (P(i));wherein the number of bits (s) in the keystream block exceeds the number of bits (b) in the ciphertext block.
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24. A method of performing symmetric encryption comprising:
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generating a keystream block (S(i)) in response to an encryption key (K), the keystream block comprising a plurality of bits (s) of a pseudo-random number sequence; and combining the keystream block (S(i)) with a plaintext block (P(i)) comprising a plurality of bits (b) to produce a ciphertext block (C(i)); wherein the number of bits (s) in the keystream block exceeds the number of bits (b) in the plaintext block. - View Dependent Claims (25, 26)
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27. A method of decrypting a symmetrically encrypted ciphertext message (C) comprising:
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generating a keystream block (S(i)) in response to a decryption key (K), the keystream block comprising a plurality of bits (s) of a pseudo-random number sequence; and combining the keystream block (S(i)) with a ciphertext block (C(i)) comprising a plurality of bits (b) to produce a plaintext block (P(i)); wherein the number of bits (s) in the keystream block exceeds the number of bits (b) in the ciphertext block.
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28. A computer program stored on a computer readable storage medium for performing symmetric encryption comprising means for generating a keystream block (S(i)) in response to an encryption key (K), the keystream block comprising a plurality of bits (s) of a pseudo-random number sequence;
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means for combining the keystream block (S(i)) with a plaintext block (P(i)) comprising a plurality of bits (b) to produce a ciphertext block (C(i)); wherein the number of bits (s) in the keystream block exceeds the number of bits (b) in the plaintext block.
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29. A computer program stored on a computer readable storage medium for decrypting a symmetrically encrypted ciphertext message (C) comprising:
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means for generating a keystream block (S(i)) in response to a decryption key (K), the keystream block comprising a plurality of bits (s) of a pseudo-random number sequence; and means for combining the keystream block (S(i)) with a ciphertext block (C(i)) comprising a plurality of bits (b) to produce a plaintext block (P(i)); wherein the number of bits (s) in the keystream block exceeds the number of bits (b) in the ciphertext block.
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Specification