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140 .IX Title "BN_mod_mul_montgomery 3"
141 .TH BN_mod_mul_montgomery 3 "0.9.7a" "2003-02-19" "OpenSSL"
144 BN_mod_mul_montgomery, BN_MONT_CTX_new, BN_MONT_CTX_init,
145 BN_MONT_CTX_free, BN_MONT_CTX_set, BN_MONT_CTX_copy,
146 BN_from_montgomery, BN_to_montgomery \- Montgomery multiplication
148 .IX Header "SYNOPSIS"
150 \& #include <openssl/bn.h>
153 \& BN_MONT_CTX *BN_MONT_CTX_new(void);
154 \& void BN_MONT_CTX_init(BN_MONT_CTX *ctx);
155 \& void BN_MONT_CTX_free(BN_MONT_CTX *mont);
158 \& int BN_MONT_CTX_set(BN_MONT_CTX *mont, const BIGNUM *m, BN_CTX *ctx);
159 \& BN_MONT_CTX *BN_MONT_CTX_copy(BN_MONT_CTX *to, BN_MONT_CTX *from);
162 \& int BN_mod_mul_montgomery(BIGNUM *r, BIGNUM *a, BIGNUM *b,
163 \& BN_MONT_CTX *mont, BN_CTX *ctx);
166 \& int BN_from_montgomery(BIGNUM *r, BIGNUM *a, BN_MONT_CTX *mont,
170 \& int BN_to_montgomery(BIGNUM *r, BIGNUM *a, BN_MONT_CTX *mont,
174 .IX Header "DESCRIPTION"
175 These functions implement Montgomery multiplication. They are used
176 automatically when BN_mod_exp(3) is called with suitable input,
177 but they may be useful when several operations are to be performed
178 using the same modulus.
180 \&\fIBN_MONT_CTX_new()\fR allocates and initializes a \fB\s-1BN_MONT_CTX\s0\fR structure.
181 \&\fIBN_MONT_CTX_init()\fR initializes an existing uninitialized \fB\s-1BN_MONT_CTX\s0\fR.
183 \&\fIBN_MONT_CTX_set()\fR sets up the \fImont\fR structure from the modulus \fIm\fR
184 by precomputing its inverse and a value R.
186 \&\fIBN_MONT_CTX_copy()\fR copies the \fB\s-1BN_MONT_CTX\s0\fR \fIfrom\fR to \fIto\fR.
188 \&\fIBN_MONT_CTX_free()\fR frees the components of the \fB\s-1BN_MONT_CTX\s0\fR, and, if
189 it was created by \fIBN_MONT_CTX_new()\fR, also the structure itself.
191 \&\fIBN_mod_mul_montgomery()\fR computes Mont(\fIa\fR,\fIb\fR):=\fIa\fR*\fIb\fR*R^\-1 and places
192 the result in \fIr\fR.
194 \&\fIBN_from_montgomery()\fR performs the Montgomery reduction \fIr\fR = \fIa\fR*R^\-1.
196 \&\fIBN_to_montgomery()\fR computes Mont(\fIa\fR,R^2), i.e. \fIa\fR*R.
197 Note that \fIa\fR must be non-negative and smaller than the modulus.
199 For all functions, \fIctx\fR is a previously allocated \fB\s-1BN_CTX\s0\fR used for
202 The \fB\s-1BN_MONT_CTX\s0\fR structure is defined as follows:
205 \& typedef struct bn_mont_ctx_st
207 \& int ri; /* number of bits in R */
208 \& BIGNUM RR; /* R^2 (used to convert to Montgomery form) */
209 \& BIGNUM N; /* The modulus */
210 \& BIGNUM Ni; /* R*(1/R mod N) - N*Ni = 1
211 \& * (Ni is only stored for bignum algorithm) */
212 \& BN_ULONG n0; /* least significant word of Ni */
216 \&\fIBN_to_montgomery()\fR is a macro.
218 .IX Header "RETURN VALUES"
219 \&\fIBN_MONT_CTX_new()\fR returns the newly allocated \fB\s-1BN_MONT_CTX\s0\fR, and \s-1NULL\s0
222 \&\fIBN_MONT_CTX_init()\fR and \fIBN_MONT_CTX_free()\fR have no return values.
224 For the other functions, 1 is returned for success, 0 on error.
225 The error codes can be obtained by ERR_get_error(3).
228 The inputs must be reduced modulo \fBm\fR, otherwise the result will be
229 outside the expected range.
231 .IX Header "SEE ALSO"
232 bn(3), ERR_get_error(3), BN_add(3),
236 \&\fIBN_MONT_CTX_new()\fR, \fIBN_MONT_CTX_free()\fR, \fIBN_MONT_CTX_set()\fR,
237 \&\fIBN_mod_mul_montgomery()\fR, \fIBN_from_montgomery()\fR and \fIBN_to_montgomery()\fR
238 are available in all versions of SSLeay and OpenSSL.
240 \&\fIBN_MONT_CTX_init()\fR and \fIBN_MONT_CTX_copy()\fR were added in SSLeay 0.9.1b.