diff --git a/lib/mpi/mpi-pow.c b/lib/mpi/mpi-pow.c
new file mode 100644
index 0000000..b04a3cf
--- /dev/null
+++ b/lib/mpi/mpi-pow.c
@@ -0,0 +1,323 @@
+/* mpi-pow.c  -  MPI functions
+ *	Copyright (C) 1994, 1996, 1998, 2000 Free Software Foundation, Inc.
+ *
+ * This file is part of GnuPG.
+ *
+ * GnuPG is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * GnuPG is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
+ *
+ * Note: This code is heavily based on the GNU MP Library.
+ *	 Actually it's the same code with only minor changes in the
+ *	 way the data is stored; this is to support the abstraction
+ *	 of an optional secure memory allocation which may be used
+ *	 to avoid revealing of sensitive data due to paging etc.
+ *	 The GNU MP Library itself is published under the LGPL;
+ *	 however I decided to publish this code under the plain GPL.
+ */
+
+#include <linux/string.h>
+#include "mpi-internal.h"
+#include "longlong.h"
+
+/****************
+ * RES = BASE ^ EXP mod MOD
+ */
+int mpi_powm(MPI res, MPI base, MPI exp, MPI mod)
+{
+	mpi_ptr_t mp_marker = NULL, bp_marker = NULL, ep_marker = NULL;
+	mpi_ptr_t xp_marker = NULL;
+	mpi_ptr_t tspace = NULL;
+	mpi_ptr_t rp, ep, mp, bp;
+	mpi_size_t esize, msize, bsize, rsize;
+	int esign, msign, bsign, rsign;
+	mpi_size_t size;
+	int mod_shift_cnt;
+	int negative_result;
+	int assign_rp = 0;
+	mpi_size_t tsize = 0;	/* to avoid compiler warning */
+	/* fixme: we should check that the warning is void */
+	int rc = -ENOMEM;
+
+	esize = exp->nlimbs;
+	msize = mod->nlimbs;
+	size = 2 * msize;
+	esign = exp->sign;
+	msign = mod->sign;
+
+	rp = res->d;
+	ep = exp->d;
+
+	if (!msize)
+		msize = 1 / msize;	/* provoke a signal */
+
+	if (!esize) {
+		/* Exponent is zero, result is 1 mod MOD, i.e., 1 or 0
+		 * depending on if MOD equals 1.  */
+		rp[0] = 1;
+		res->nlimbs = (msize == 1 && mod->d[0] == 1) ? 0 : 1;
+		res->sign = 0;
+		goto leave;
+	}
+
+	/* Normalize MOD (i.e. make its most significant bit set) as required by
+	 * mpn_divrem.  This will make the intermediate values in the calculation
+	 * slightly larger, but the correct result is obtained after a final
+	 * reduction using the original MOD value.  */
+	mp = mp_marker = mpi_alloc_limb_space(msize);
+	if (!mp)
+		goto enomem;
+	count_leading_zeros(mod_shift_cnt, mod->d[msize - 1]);
+	if (mod_shift_cnt)
+		mpihelp_lshift(mp, mod->d, msize, mod_shift_cnt);
+	else
+		MPN_COPY(mp, mod->d, msize);
+
+	bsize = base->nlimbs;
+	bsign = base->sign;
+	if (bsize > msize) {	/* The base is larger than the module. Reduce it. */
+		/* Allocate (BSIZE + 1) with space for remainder and quotient.
+		 * (The quotient is (bsize - msize + 1) limbs.)  */
+		bp = bp_marker = mpi_alloc_limb_space(bsize + 1);
+		if (!bp)
+			goto enomem;
+		MPN_COPY(bp, base->d, bsize);
+		/* We don't care about the quotient, store it above the remainder,
+		 * at BP + MSIZE.  */
+		mpihelp_divrem(bp + msize, 0, bp, bsize, mp, msize);
+		bsize = msize;
+		/* Canonicalize the base, since we are going to multiply with it
+		 * quite a few times.  */
+		MPN_NORMALIZE(bp, bsize);
+	} else
+		bp = base->d;
+
+	if (!bsize) {
+		res->nlimbs = 0;
+		res->sign = 0;
+		goto leave;
+	}
+
+	if (res->alloced < size) {
+		/* We have to allocate more space for RES.  If any of the input
+		 * parameters are identical to RES, defer deallocation of the old
+		 * space.  */
+		if (rp == ep || rp == mp || rp == bp) {
+			rp = mpi_alloc_limb_space(size);
+			if (!rp)
+				goto enomem;
+			assign_rp = 1;
+		} else {
+			if (mpi_resize(res, size) < 0)
+				goto enomem;
+			rp = res->d;
+		}
+	} else {		/* Make BASE, EXP and MOD not overlap with RES.  */
+		if (rp == bp) {
+			/* RES and BASE are identical.  Allocate temp. space for BASE.  */
+			BUG_ON(bp_marker);
+			bp = bp_marker = mpi_alloc_limb_space(bsize);
+			if (!bp)
+				goto enomem;
+			MPN_COPY(bp, rp, bsize);
+		}
+		if (rp == ep) {
+			/* RES and EXP are identical.  Allocate temp. space for EXP.  */
+			ep = ep_marker = mpi_alloc_limb_space(esize);
+			if (!ep)
+				goto enomem;
+			MPN_COPY(ep, rp, esize);
+		}
+		if (rp == mp) {
+			/* RES and MOD are identical.  Allocate temporary space for MOD. */
+			BUG_ON(mp_marker);
+			mp = mp_marker = mpi_alloc_limb_space(msize);
+			if (!mp)
+				goto enomem;
+			MPN_COPY(mp, rp, msize);
+		}
+	}
+
+	MPN_COPY(rp, bp, bsize);
+	rsize = bsize;
+	rsign = bsign;
+
+	{
+		mpi_size_t i;
+		mpi_ptr_t xp;
+		int c;
+		mpi_limb_t e;
+		mpi_limb_t carry_limb;
+		struct karatsuba_ctx karactx;
+
+		xp = xp_marker = mpi_alloc_limb_space(2 * (msize + 1));
+		if (!xp)
+			goto enomem;
+
+		memset(&karactx, 0, sizeof karactx);
+		negative_result = (ep[0] & 1) && base->sign;
+
+		i = esize - 1;
+		e = ep[i];
+		count_leading_zeros(c, e);
+		e = (e << c) << 1;	/* shift the exp bits to the left, lose msb */
+		c = BITS_PER_MPI_LIMB - 1 - c;
+
+		/* Main loop.
+		 *
+		 * Make the result be pointed to alternately by XP and RP.  This
+		 * helps us avoid block copying, which would otherwise be necessary
+		 * with the overlap restrictions of mpihelp_divmod. With 50% probability
+		 * the result after this loop will be in the area originally pointed
+		 * by RP (==RES->d), and with 50% probability in the area originally
+		 * pointed to by XP.
+		 */
+
+		for (;;) {
+			while (c) {
+				mpi_ptr_t tp;
+				mpi_size_t xsize;
+
+				/*if (mpihelp_mul_n(xp, rp, rp, rsize) < 0) goto enomem */
+				if (rsize < KARATSUBA_THRESHOLD)
+					mpih_sqr_n_basecase(xp, rp, rsize);
+				else {
+					if (!tspace) {
+						tsize = 2 * rsize;
+						tspace =
+						    mpi_alloc_limb_space(tsize);
+						if (!tspace)
+							goto enomem;
+					} else if (tsize < (2 * rsize)) {
+						mpi_free_limb_space(tspace);
+						tsize = 2 * rsize;
+						tspace =
+						    mpi_alloc_limb_space(tsize);
+						if (!tspace)
+							goto enomem;
+					}
+					mpih_sqr_n(xp, rp, rsize, tspace);
+				}
+
+				xsize = 2 * rsize;
+				if (xsize > msize) {
+					mpihelp_divrem(xp + msize, 0, xp, xsize,
+						       mp, msize);
+					xsize = msize;
+				}
+
+				tp = rp;
+				rp = xp;
+				xp = tp;
+				rsize = xsize;
+
+				if ((mpi_limb_signed_t) e < 0) {
+					/*mpihelp_mul( xp, rp, rsize, bp, bsize ); */
+					if (bsize < KARATSUBA_THRESHOLD) {
+						mpi_limb_t tmp;
+						if (mpihelp_mul
+						    (xp, rp, rsize, bp, bsize,
+						     &tmp) < 0)
+							goto enomem;
+					} else {
+						if (mpihelp_mul_karatsuba_case
+						    (xp, rp, rsize, bp, bsize,
+						     &karactx) < 0)
+							goto enomem;
+					}
+
+					xsize = rsize + bsize;
+					if (xsize > msize) {
+						mpihelp_divrem(xp + msize, 0,
+							       xp, xsize, mp,
+							       msize);
+						xsize = msize;
+					}
+
+					tp = rp;
+					rp = xp;
+					xp = tp;
+					rsize = xsize;
+				}
+				e <<= 1;
+				c--;
+			}
+
+			i--;
+			if (i < 0)
+				break;
+			e = ep[i];
+			c = BITS_PER_MPI_LIMB;
+		}
+
+		/* We shifted MOD, the modulo reduction argument, left MOD_SHIFT_CNT
+		 * steps.  Adjust the result by reducing it with the original MOD.
+		 *
+		 * Also make sure the result is put in RES->d (where it already
+		 * might be, see above).
+		 */
+		if (mod_shift_cnt) {
+			carry_limb =
+			    mpihelp_lshift(res->d, rp, rsize, mod_shift_cnt);
+			rp = res->d;
+			if (carry_limb) {
+				rp[rsize] = carry_limb;
+				rsize++;
+			}
+		} else {
+			MPN_COPY(res->d, rp, rsize);
+			rp = res->d;
+		}
+
+		if (rsize >= msize) {
+			mpihelp_divrem(rp + msize, 0, rp, rsize, mp, msize);
+			rsize = msize;
+		}
+
+		/* Remove any leading zero words from the result.  */
+		if (mod_shift_cnt)
+			mpihelp_rshift(rp, rp, rsize, mod_shift_cnt);
+		MPN_NORMALIZE(rp, rsize);
+
+		mpihelp_release_karatsuba_ctx(&karactx);
+	}
+
+	if (negative_result && rsize) {
+		if (mod_shift_cnt)
+			mpihelp_rshift(mp, mp, msize, mod_shift_cnt);
+		mpihelp_sub(rp, mp, msize, rp, rsize);
+		rsize = msize;
+		rsign = msign;
+		MPN_NORMALIZE(rp, rsize);
+	}
+	res->nlimbs = rsize;
+	res->sign = rsign;
+
+leave:
+	rc = 0;
+enomem:
+	if (assign_rp)
+		mpi_assign_limb_space(res, rp, size);
+	if (mp_marker)
+		mpi_free_limb_space(mp_marker);
+	if (bp_marker)
+		mpi_free_limb_space(bp_marker);
+	if (ep_marker)
+		mpi_free_limb_space(ep_marker);
+	if (xp_marker)
+		mpi_free_limb_space(xp_marker);
+	if (tspace)
+		mpi_free_limb_space(tspace);
+	return rc;
+}
+EXPORT_SYMBOL_GPL(mpi_powm);