In cryptography, blinding is a technique by which an agent can provide a service to (i.e, compute a function for) a client in an encoded form without knowing either the real input or the real output.
More precisely, Alice has an input x and Oscar has a function f. Alice would like Oscar to compute y = f(x) for her without revealing either x or y to him. The reason for her wanting this might be that she doesn't know the function f or that she does not have the resources to compute it. Alice "blinds" the message by encoding it into some other input E(x); the encoding E must be a bijection on the input space of f, ideally a random permutation. Oscar gives her f(E(x)), to which she applies a decoding D to obtain D(f(E(x))) = y.
Of course, not all functions admit of blind computation.
The most common application of blinding is the blind signature. In a blind signature protocol the signer digitally signs a message without being able to learn its content.
The one-time pad is an application of blinding to the secure communication problem. Alice would like to send a message to Bob secretly, however all of their communication can be read by Oscar. Therefore Alice sends the message after blinding it with a secret key or pad that she shares with Bob. Bob reverses the blinding after receiving the message. In this example, the function f is the identity and E and D are both typically the XOR operation.
The term "blindness" also applies to partial visualimpairment: In North America and most of Europe, legal blindness is defined as vision of 20/200 (6/60) or less in the better eye with correction.
Historically, blind and visually impaired people have either been treated as if their lack of sight were an outward manifestation of some internal lack of reason, or as if they possessed extra-sensory abilities.
The authors of modern educational materials (see: blindness and education for further reading on that subject), as well as those treating blindness in literature, have worked to paint a truer picture of blind people as three-dimensional individuals with a range of abilities, talents, and even character flaws.
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