Update files for OpenSSL-1.0.0f import.
[dragonfly.git] / secure / lib / libcrypto / man / BN_mod_mul_montgomery.3
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124.\" ========================================================================
125.\"
126.IX Title "BN_mod_mul_montgomery 3"
e3261593 127.TH BN_mod_mul_montgomery 3 "2012-01-04" "1.0.0f" "OpenSSL"
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128.\" For nroff, turn off justification. Always turn off hyphenation; it makes
129.\" way too many mistakes in technical documents.
130.if n .ad l
131.nh
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132.SH "NAME"
133BN_mod_mul_montgomery, BN_MONT_CTX_new, BN_MONT_CTX_init,
134BN_MONT_CTX_free, BN_MONT_CTX_set, BN_MONT_CTX_copy,
135BN_from_montgomery, BN_to_montgomery \- Montgomery multiplication
136.SH "SYNOPSIS"
8b0cefbb 137.IX Header "SYNOPSIS"
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138.Vb 1
139\& #include <openssl/bn.h>
e257b235 140\&
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141\& BN_MONT_CTX *BN_MONT_CTX_new(void);
142\& void BN_MONT_CTX_init(BN_MONT_CTX *ctx);
143\& void BN_MONT_CTX_free(BN_MONT_CTX *mont);
e257b235 144\&
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145\& int BN_MONT_CTX_set(BN_MONT_CTX *mont, const BIGNUM *m, BN_CTX *ctx);
146\& BN_MONT_CTX *BN_MONT_CTX_copy(BN_MONT_CTX *to, BN_MONT_CTX *from);
e257b235 147\&
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148\& int BN_mod_mul_montgomery(BIGNUM *r, BIGNUM *a, BIGNUM *b,
149\& BN_MONT_CTX *mont, BN_CTX *ctx);
e257b235 150\&
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151\& int BN_from_montgomery(BIGNUM *r, BIGNUM *a, BN_MONT_CTX *mont,
152\& BN_CTX *ctx);
e257b235 153\&
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154\& int BN_to_montgomery(BIGNUM *r, BIGNUM *a, BN_MONT_CTX *mont,
155\& BN_CTX *ctx);
156.Ve
157.SH "DESCRIPTION"
8b0cefbb 158.IX Header "DESCRIPTION"
984263bc 159These functions implement Montgomery multiplication. They are used
8b0cefbb 160automatically when \fIBN_mod_exp\fR\|(3) is called with suitable input,
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161but they may be useful when several operations are to be performed
162using the same modulus.
163.PP
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164\&\fIBN_MONT_CTX_new()\fR allocates and initializes a \fB\s-1BN_MONT_CTX\s0\fR structure.
165\&\fIBN_MONT_CTX_init()\fR initializes an existing uninitialized \fB\s-1BN_MONT_CTX\s0\fR.
984263bc 166.PP
8b0cefbb 167\&\fIBN_MONT_CTX_set()\fR sets up the \fImont\fR structure from the modulus \fIm\fR
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168by precomputing its inverse and a value R.
169.PP
8b0cefbb 170\&\fIBN_MONT_CTX_copy()\fR copies the \fB\s-1BN_MONT_CTX\s0\fR \fIfrom\fR to \fIto\fR.
984263bc 171.PP
8b0cefbb 172\&\fIBN_MONT_CTX_free()\fR frees the components of the \fB\s-1BN_MONT_CTX\s0\fR, and, if
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173it was created by \fIBN_MONT_CTX_new()\fR, also the structure itself.
174.PP
8b0cefbb 175\&\fIBN_mod_mul_montgomery()\fR computes Mont(\fIa\fR,\fIb\fR):=\fIa\fR*\fIb\fR*R^\-1 and places
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176the result in \fIr\fR.
177.PP
8b0cefbb 178\&\fIBN_from_montgomery()\fR performs the Montgomery reduction \fIr\fR = \fIa\fR*R^\-1.
984263bc 179.PP
8b0cefbb 180\&\fIBN_to_montgomery()\fR computes Mont(\fIa\fR,R^2), i.e. \fIa\fR*R.
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181Note that \fIa\fR must be non-negative and smaller than the modulus.
182.PP
8b0cefbb 183For all functions, \fIctx\fR is a previously allocated \fB\s-1BN_CTX\s0\fR used for
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184temporary variables.
185.PP
8b0cefbb 186The \fB\s-1BN_MONT_CTX\s0\fR structure is defined as follows:
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187.PP
188.Vb 10
189\& typedef struct bn_mont_ctx_st
190\& {
191\& int ri; /* number of bits in R */
192\& BIGNUM RR; /* R^2 (used to convert to Montgomery form) */
193\& BIGNUM N; /* The modulus */
e257b235 194\& BIGNUM Ni; /* R*(1/R mod N) \- N*Ni = 1
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195\& * (Ni is only stored for bignum algorithm) */
196\& BN_ULONG n0; /* least significant word of Ni */
197\& int flags;
198\& } BN_MONT_CTX;
199.Ve
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200.PP
201\&\fIBN_to_montgomery()\fR is a macro.
984263bc 202.SH "RETURN VALUES"
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203.IX Header "RETURN VALUES"
204\&\fIBN_MONT_CTX_new()\fR returns the newly allocated \fB\s-1BN_MONT_CTX\s0\fR, and \s-1NULL\s0
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205on error.
206.PP
8b0cefbb 207\&\fIBN_MONT_CTX_init()\fR and \fIBN_MONT_CTX_free()\fR have no return values.
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208.PP
209For the other functions, 1 is returned for success, 0 on error.
8b0cefbb 210The error codes can be obtained by \fIERR_get_error\fR\|(3).
984263bc 211.SH "WARNING"
8b0cefbb 212.IX Header "WARNING"
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213The inputs must be reduced modulo \fBm\fR, otherwise the result will be
214outside the expected range.
215.SH "SEE ALSO"
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216.IX Header "SEE ALSO"
217\&\fIbn\fR\|(3), \fIERR_get_error\fR\|(3), \fIBN_add\fR\|(3),
218\&\fIBN_CTX_new\fR\|(3)
984263bc 219.SH "HISTORY"
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220.IX Header "HISTORY"
221\&\fIBN_MONT_CTX_new()\fR, \fIBN_MONT_CTX_free()\fR, \fIBN_MONT_CTX_set()\fR,
222\&\fIBN_mod_mul_montgomery()\fR, \fIBN_from_montgomery()\fR and \fIBN_to_montgomery()\fR
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223are available in all versions of SSLeay and OpenSSL.
224.PP
8b0cefbb 225\&\fIBN_MONT_CTX_init()\fR and \fIBN_MONT_CTX_copy()\fR were added in SSLeay 0.9.1b.