323 lines
12 KiB
Groff
Executable File
323 lines
12 KiB
Groff
Executable File
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.\" ========================================================================
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.\"
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.IX Title "EC_GROUP_NEW 3"
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.TH EC_GROUP_NEW 3 "2020-03-02" "3.0.0-dev" "OpenSSL"
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.\" For nroff, turn off justification. Always turn off hyphenation; it makes
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.\" way too many mistakes in technical documents.
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.if n .ad l
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.nh
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.SH "NAME"
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EC_GROUP_get_ecparameters,
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EC_GROUP_get_ecpkparameters,
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EC_GROUP_new_ex,
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EC_GROUP_new,
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EC_GROUP_new_from_ecparameters,
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EC_GROUP_new_from_ecpkparameters,
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EC_GROUP_free,
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EC_GROUP_clear_free,
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EC_GROUP_new_curve_GFp,
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EC_GROUP_new_curve_GF2m,
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EC_GROUP_new_by_curve_name_ex,
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EC_GROUP_new_by_curve_name,
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EC_GROUP_set_curve,
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EC_GROUP_get_curve,
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EC_GROUP_set_curve_GFp,
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EC_GROUP_get_curve_GFp,
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EC_GROUP_set_curve_GF2m,
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EC_GROUP_get_curve_GF2m,
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EC_get_builtin_curves \- Functions for creating and destroying EC_GROUP
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objects
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.SH "SYNOPSIS"
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.IX Header "SYNOPSIS"
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.Vb 1
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\& #include <openssl/ec.h>
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\&
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\& EC_GROUP *EC_GROUP_new_ex(OPENSSL_CTX *libctx, const EC_METHOD *meth);
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\& EC_GROUP *EC_GROUP_new(const EC_METHOD *meth);
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\& EC_GROUP *EC_GROUP_new_from_ecparameters(const ECPARAMETERS *params)
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\& EC_GROUP *EC_GROUP_new_from_ecpkparameters(const ECPKPARAMETERS *params)
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\& void EC_GROUP_free(EC_GROUP *group);
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\&
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\& EC_GROUP *EC_GROUP_new_curve_GFp(const BIGNUM *p, const BIGNUM *a,
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\& const BIGNUM *b, BN_CTX *ctx);
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\& EC_GROUP *EC_GROUP_new_curve_GF2m(const BIGNUM *p, const BIGNUM *a,
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\& const BIGNUM *b, BN_CTX *ctx);
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\& EC_GROUP *EC_GROUP_new_by_curve_name_ex(OPENSSL_CTX *libctx, int nid);
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\& EC_GROUP *EC_GROUP_new_by_curve_name(int nid);
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\&
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\& int EC_GROUP_set_curve(EC_GROUP *group, const BIGNUM *p, const BIGNUM *a,
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\& const BIGNUM *b, BN_CTX *ctx);
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\& int EC_GROUP_get_curve(const EC_GROUP *group, BIGNUM *p, BIGNUM *a, BIGNUM *b,
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\& BN_CTX *ctx);
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\& int EC_GROUP_set_curve_GFp(EC_GROUP *group, const BIGNUM *p,
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\& const BIGNUM *a, const BIGNUM *b, BN_CTX *ctx);
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\& int EC_GROUP_get_curve_GFp(const EC_GROUP *group, BIGNUM *p,
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\& BIGNUM *a, BIGNUM *b, BN_CTX *ctx);
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\& int EC_GROUP_set_curve_GF2m(EC_GROUP *group, const BIGNUM *p,
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\& const BIGNUM *a, const BIGNUM *b, BN_CTX *ctx);
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\& int EC_GROUP_get_curve_GF2m(const EC_GROUP *group, BIGNUM *p,
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\& BIGNUM *a, BIGNUM *b, BN_CTX *ctx);
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\&
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\& ECPARAMETERS *EC_GROUP_get_ecparameters(const EC_GROUP *group, ECPARAMETERS *params)
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\& ECPKPARAMETERS *EC_GROUP_get_ecpkparameters(const EC_GROUP *group, ECPKPARAMETERS *params)
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\&
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\& size_t EC_get_builtin_curves(EC_builtin_curve *r, size_t nitems);
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.Ve
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.PP
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Deprecated since OpenSSL 3.0, can be hidden entirely by defining
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\&\fB\s-1OPENSSL_API_COMPAT\s0\fR with a suitable version value, see
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\&\fIopenssl_user_macros\fR\|(7):
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.PP
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.Vb 1
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\& void EC_GROUP_clear_free(EC_GROUP *group);
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.Ve
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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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Within the library there are two forms of elliptic curve that are of interest.
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The first form is those defined over the prime field Fp. The elements of Fp are
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the integers 0 to p\-1, where p is a prime number. This gives us a revised
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elliptic curve equation as follows:
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.PP
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y^2 mod p = x^3 +ax + b mod p
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.PP
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The second form is those defined over a binary field F2^m where the elements of
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the field are integers of length at most m bits. For this form the elliptic
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curve equation is modified to:
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.PP
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y^2 + xy = x^3 + ax^2 + b (where b != 0)
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.PP
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Operations in a binary field are performed relative to an
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\&\fBirreducible polynomial\fR. All such curves with OpenSSL use a trinomial or a
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pentanomial for this parameter.
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.PP
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A new curve can be constructed by calling \fIEC_GROUP_new_ex()\fR, using the
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implementation provided by \fBmeth\fR (see \fIEC_GFp_simple_method\fR\|(3)) and
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associated with the library context \fBctx\fR (see \s-1\fIOPENSSL_CTX\s0\fR\|(3)).
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The \fBctx\fR parameter may be \s-1NULL\s0 in which case the default library context is
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used.
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It is then necessary to call \fIEC_GROUP_set_curve()\fR to set the curve parameters.
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\&\fIEC_GROUP_new_from_ecparameters()\fR will create a group from the
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specified \fBparams\fR and
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\&\fIEC_GROUP_new_from_ecpkparameters()\fR will create a group from the specific \s-1PK\s0
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\&\fBparams\fR.
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.PP
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\&\fIEC_GROUP_new()\fR is the same as \fIEC_GROUP_new_ex()\fR except that the library context
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used is always the default library context.
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.PP
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\&\fIEC_GROUP_set_curve()\fR sets the curve parameters \fBp\fR, \fBa\fR and \fBb\fR. For a curve
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over Fp \fBp\fR is the prime for the field. For a curve over F2^m \fBp\fR represents
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the irreducible polynomial \- each bit represents a term in the polynomial.
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Therefore there will either be three or five bits set dependent on whether the
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polynomial is a trinomial or a pentanomial.
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In either case, \fBa\fR and \fBb\fR represents the coefficients a and b from the
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relevant equation introduced above.
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.PP
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\&\fIEC_group_get_curve()\fR obtains the previously set curve parameters.
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.PP
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\&\fIEC_GROUP_set_curve_GFp()\fR and \fIEC_GROUP_set_curve_GF2m()\fR are synonyms for
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\&\fIEC_GROUP_set_curve()\fR. They are defined for backwards compatibility only and
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should not be used.
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.PP
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\&\fIEC_GROUP_get_curve_GFp()\fR and \fIEC_GROUP_get_curve_GF2m()\fR are synonyms for
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\&\fIEC_GROUP_get_curve()\fR. They are defined for backwards compatibility only and
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should not be used.
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.PP
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The functions \fIEC_GROUP_new_curve_GFp()\fR and \fIEC_GROUP_new_curve_GF2m()\fR are
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shortcuts for calling \fIEC_GROUP_new()\fR and then the \fIEC_GROUP_set_curve()\fR function.
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An appropriate default implementation method will be used.
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.PP
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Whilst the library can be used to create any curve using the functions described
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above, there are also a number of predefined curves that are available. In order
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to obtain a list of all of the predefined curves, call the function
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\&\fIEC_get_builtin_curves()\fR. The parameter \fBr\fR should be an array of
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EC_builtin_curve structures of size \fBnitems\fR. The function will populate the
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\&\fBr\fR array with information about the built-in curves. If \fBnitems\fR is less than
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the total number of curves available, then the first \fBnitems\fR curves will be
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returned. Otherwise the total number of curves will be provided. The return
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value is the total number of curves available (whether that number has been
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populated in \fBr\fR or not). Passing a \s-1NULL\s0 \fBr\fR, or setting \fBnitems\fR to 0 will
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do nothing other than return the total number of curves available.
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The EC_builtin_curve structure is defined as follows:
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.PP
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.Vb 4
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\& typedef struct {
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\& int nid;
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\& const char *comment;
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\& } EC_builtin_curve;
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.Ve
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.PP
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Each EC_builtin_curve item has a unique integer id (\fBnid\fR), and a human
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readable comment string describing the curve.
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.PP
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In order to construct a built-in curve use the function
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\&\fIEC_GROUP_new_by_curve_name_ex()\fR and provide the \fBnid\fR of the curve to be
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constructed and the associated library context to be used in \fBctx\fR (see
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\&\s-1\fIOPENSSL_CTX\s0\fR\|(3)). The \fBctx\fR value may be \s-1NULL\s0 in which case the default
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library context is used.
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.PP
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\&\fIEC_GROUP_new_by_curve_name()\fR is the same as \fIEC_GROUP_new_by_curve_name_ex()\fR
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except that the default library context is always used.
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.PP
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\&\fIEC_GROUP_free()\fR frees the memory associated with the \s-1EC_GROUP\s0.
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If \fBgroup\fR is \s-1NULL\s0 nothing is done.
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.PP
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\&\fIEC_GROUP_clear_free()\fR is deprecated: it was meant to destroy any sensitive data
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held within the \s-1EC_GROUP\s0 and then free its memory, but since all the data stored
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in the \s-1EC_GROUP\s0 is public anyway, this function is unnecessary.
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Its use can be safely replaced with \fIEC_GROUP_free()\fR.
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If \fBgroup\fR is \s-1NULL\s0 nothing is done.
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.SH "RETURN VALUES"
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.IX Header "RETURN VALUES"
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All EC_GROUP_new* functions return a pointer to the newly constructed group, or
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\&\s-1NULL\s0 on error.
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.PP
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\&\fIEC_get_builtin_curves()\fR returns the number of built-in curves that are
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available.
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.PP
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\&\fIEC_GROUP_set_curve_GFp()\fR, \fIEC_GROUP_get_curve_GFp()\fR, \fIEC_GROUP_set_curve_GF2m()\fR,
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\&\fIEC_GROUP_get_curve_GF2m()\fR return 1 on success or 0 on error.
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.SH "SEE ALSO"
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.IX Header "SEE ALSO"
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\&\fIcrypto\fR\|(7), \fIEC_GROUP_copy\fR\|(3),
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\&\fIEC_POINT_new\fR\|(3), \fIEC_POINT_add\fR\|(3), \fIEC_KEY_new\fR\|(3),
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\&\fIEC_GFp_simple_method\fR\|(3), \fId2i_ECPKParameters\fR\|(3),
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\&\s-1\fIOPENSSL_CTX\s0\fR\|(3)
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.SH "HISTORY"
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.IX Header "HISTORY"
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.IP "\(bu" 2
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\&\fIEC_GROUP_new_ex()\fR and \fIEC_GROUP_new_by_curve_name_ex()\fR were added in OpenSSL 3.0.
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.IP "\(bu" 2
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\&\fIEC_GROUP_clear_free()\fR was deprecated in OpenSSL 3.0; use \fIEC_GROUP_free()\fR
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instead.
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.SH "COPYRIGHT"
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.IX Header "COPYRIGHT"
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Copyright 2013\-2018 The OpenSSL Project Authors. All Rights Reserved.
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.PP
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Licensed under the Apache License 2.0 (the \*(L"License\*(R"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file \s-1LICENSE\s0 in the source distribution or at
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<https://www.openssl.org/source/license.html>.
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