Limits RegistryPUBLIC RECORD
Limits RegistryIn his 1949 paper 'Communication Theory of Secrecy Systems,' Claude Shannon proved that perfect secrecy is achievable only when the key is at least as long as the message and never reused — exactly satisfied by the one-time pad cipher, first proposed decades earlier by Gilbert Vernam. This remains the only encryption scheme ever proven unconditionally, mathematically unbreakable regardless of an attacker's computing power, in contrast to every modern practical cipher (AES, RSA, etc.), whose security instead rests on computational hardness assumptions.
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In his 1949 paper 'Communication Theory of Secrecy Systems,' Claude Shannon proved that perfect secrecy is achievable only when the key is at least as long as the message and never reused — exactly satisfied by the one-time pad cipher, first proposed decades earlier by Gilbert Vernam. This remains the only encryption scheme ever proven unconditionally, mathematically unbreakable regardless of an attacker's computing power, in contrast to every modern practical cipher (AES, RSA, etc.), whose security instead rests on computational hardness assumptions.
Claude Shannon's 1949 theorem proves that a symmetric-key cipher can achieve perfect secrecy — ciphertext statistically independent of the plaintext — only if the secret key is at least as long as the message and used exactly once, as realized by the one-time pad.
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Current frontiers derived from accepted Claims.
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The frontier as it changed over time.
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1 accepted Claim, with 1 linked evidence records.
Permanent ID limitsregistry.com/limits/LR-SHANNON-PERFECT-SECRECY-KEY-LENGTH
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Limits Registry. LR-SHANNON-PERFECT-SECRECY-KEY-LENGTH. Minimum key length required for information-theoretically perfect secrecy. 2026.