Soit$T$un courant positif fermé sur un voisinage de 0 dans$C$^{n}. Nous montrons que$T$admet un cône tangent (limite de la famille de ses homothétiques), dès que les masses projectives$v$_{T}(r) convergent assez vite vers$V$_{T}(0) pour que ($v$_{T}(r)−$v$_{T}(0))/$r$soit localement sommable en$r$=0. Cette condition suffisante est optimale: nous construisons des courants de bidegré (1, 1) n'ayant pas de cône tangent, tels que l'intégrale de ($v$_{T}(r)−$v$_{T}(0))/$r$soit aussi peu divergente qu'on le souhaite. Lorsque$T$est le courant d'intégration sur un ensemble analytique, on vérifie que$v$_{T}(r)−$v$_{T}(0)=0$r$^{ε}), ce qui redonne le théorème de Thie-King sur l'existence du cône tangent.

We present a multivariate version of Hidden Field Equations (HFE) over a finite field of odd characteristic, with an extra "embedding'' modifier. Combining these known ideas makes our new MPKC (multivariate public key cryptosystem) more efficient and scalable than any other extant multivariate encryption scheme. Switching to odd characteristics in HFE-like schemes affects how an attacker can make use of field equations. Extensive empirical tests (using MAGMA-2.14, the best commercially available \mathbold{F_4} implementation) suggests that our new construction is indeed secure against algebraic attacks using Gröbner Basis algorithms. The "embedding'' serves both to narrow down choices of pre-images and to guard against a possible Kipnis-Shamir type (rank-based) attack. We may hence reasonably argue that for practical sizes, prior attacks take exponential time. We demonstrate that our construction is in fact efficient by implementing practical-sized examples of our "odd-char HFE'' with 3 variables (`"THFE'') over GF(31). To be precise, our preliminary THFE implementation is 15x--20x the speed of RSA-1024.

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