. The use of cryptographic devices as "black boxes", namely trusting their internal designs, has been suggested and in fact Capstone technology is offered as a next generation hardware-protected escrow encryption technology. Software cryptographic servers and programs are being offered as well, for use as library functions, as cryptography gets more and more prevalent in computing environments. The question we address in this paper is how the usage of cryptography as a black box exposes users to various threats and attacks that are undetectable in a black-box environment. We present the SETUP (Secretly Embedded Trapdoor with Universal Protection) mechanism, which can be embedded in a cryptographic black-box device. It enables an attacker (the manufacturer) to get the user's secret (from some stage of the output process of the device) in an unnoticeable fashion, yet protects against attacks by others and against reverse engineering (thus, maintaining the relative advantage of the actual...

Abstract. We consider a problem which was stated in a request for comments made by NIST in the FIPS97 document. The question is the following: Can we have a digital signature public key infrastructure where the public (signature verification) keys cannot be abused for performing encryption? This may be applicable in the context of, say, exportable/escrow cryptography. The basic dilemma is that on the one hand, (1) to avoid framing by potentially misbehaving authorities we do not want them to ever learn the “signing keys ” (e.g., Japan at some point declared a policy where signature keys may be required to be escrowed), and on the other hand (2) if we allow separate inaccessible public signatureverificationkeys,thesekeys(basedontrapdoorfunctions)canbe used as “shadow public-keys, ” and hence can be used to encrypt data in an unrecoverable manner. Any solution within the “trapdoor function” paradigm of Diffie and Hellman does not seem to lead to a solution which will simultaneously satisfy (1) and (2). The cryptographic community so far has paid very limited attention to