297 lines
11 KiB
Plaintext
297 lines
11 KiB
Plaintext
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.\" ========================================================================
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.\"
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.IX Title "COMP_CTX_NEW 3ossl"
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.TH COMP_CTX_NEW 3ossl "2024-01-30" "3.2.1" "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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COMP_CTX_new,
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COMP_CTX_get_method,
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COMP_CTX_get_type,
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COMP_get_type,
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COMP_get_name,
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COMP_CTX_free,
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COMP_compress_block,
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COMP_expand_block,
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COMP_zlib,
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COMP_zlib_oneshot,
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COMP_brotli,
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COMP_brotli_oneshot,
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COMP_zstd,
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COMP_zstd_oneshot,
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BIO_f_zlib,
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BIO_f_brotli,
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BIO_f_zstd
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\&\- Compression support
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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/comp.h>
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\&
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\& COMP_CTX *COMP_CTX_new(COMP_METHOD *meth);
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\& void COMP_CTX_free(COMP_CTX *ctx);
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\& const COMP_METHOD *COMP_CTX_get_method(const COMP_CTX *ctx);
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\& int COMP_CTX_get_type(const COMP_CTX* comp);
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\& int COMP_get_type(const COMP_METHOD *meth);
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\& const char *COMP_get_name(const COMP_METHOD *meth);
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\&
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\& int COMP_compress_block(COMP_CTX *ctx, unsigned char *out, int olen,
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\& unsigned char *in, int ilen);
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\& int COMP_expand_block(COMP_CTX *ctx, unsigned char *out, int olen,
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\& unsigned char *in, int ilen);
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\&
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\& COMP_METHOD *COMP_zlib(void);
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\& COMP_METHOD *COMP_zlib_oneshot(void);
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\& COMP_METHOD *COMP_brotli(void);
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\& COMP_METHOD *COMP_brotli_oneshot(void);
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\& COMP_METHOD *COMP_zstd(void);
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\& COMP_METHOD *COMP_zstd_oneshot(void);
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\&
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\& const BIO_METHOD *BIO_f_zlib(void);
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\& const BIO_METHOD *BIO_f_brotli(void);
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\& const BIO_METHOD *BIO_f_zstd(void);
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.Ve
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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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These functions provide compression support for OpenSSL. Compression is used within
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the OpenSSL library to support \s-1TLS\s0 record and certificate compression.
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.PP
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\&\fICOMP_CTX_new()\fR is used to create a new \fB\s-1COMP_CTX\s0\fR structure used to compress data.
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\&\fICOMP_CTX_free()\fR is used to free the returned \fB\s-1COMP_CTX\s0\fR.
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.PP
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\&\fICOMP_CTX_get_method()\fR returns the \fB\s-1COMP_METHOD\s0\fR of the given \fIctx\fR.
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.PP
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\&\fICOMP_CTX_get_type()\fR and \fICOMP_get_type()\fR return the \s-1NID\s0 for the \fB\s-1COMP_CTX\s0\fR and
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\&\fB\s-1COMP_METHOD\s0\fR, respectively. \fICOMP_get_name()\fR returns the name of the algorithm
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of the given \fB\s-1COMP_METHOD\s0\fR.
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.PP
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\&\fICOMP_compress_block()\fR compresses b<ilen> bytes from the buffer \fIin\fR into the
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buffer b<out> of size \fIolen\fR using the algorithm specified by \fIctx\fR.
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.PP
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\&\fICOMP_expand_block()\fR expands \fIilen\fR bytes from the buffer \fIin\fR into the
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buffer \fIout\fR of size \fIolen\fR using the algorithm specified by \fIctx\fR.
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.PP
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Methods (\fB\s-1COMP_METHOD\s0\fR) may be specified by one of these functions. These functions
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will be available even if their corresponding compression algorithm is not configured
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into the OpenSSL library. In such a case, \s-1NULL\s0 will be returned.
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.IP "\(bu" 4
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\&\fICOMP_zlib()\fR returns a \fB\s-1COMP_METHOD\s0\fR for stream-based \s-1ZLIB\s0 compression.
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.IP "\(bu" 4
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\&\fICOMP_zlib_oneshot()\fR returns a \fB\s-1COMP_METHOD\s0\fR for one-shot \s-1ZLIB\s0 compression.
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.IP "\(bu" 4
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\&\fICOMP_brotli()\fR returns a \fB\s-1COMP_METHOD\s0\fR for stream-based Brotli compression.
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.IP "\(bu" 4
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\&\fICOMP_brotli_oneshot()\fR returns a \fB\s-1COMP_METHOD\s0\fR for one-shot Brotli compression.
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.IP "\(bu" 4
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\&\fICOMP_zstd()\fR returns a \fB\s-1COMP_METHOD\s0\fR for stream-based Zstandard compression.
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.IP "\(bu" 4
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\&\fICOMP_zstd_oneshot()\fR returns a \fB\s-1COMP_METHOD\s0\fR for one-shot Zstandard compression.
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.PP
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\&\fIBIO_f_zlib()\fR, \fIBIO_f_brotli()\fR \fIBIO_f_zstd()\fR each return a \fB\s-1BIO_METHOD\s0\fR that may be used to
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create a \fB\s-1BIO\s0\fR via \fB\f(BIBIO_new\fB\|(3)\fR to read and write compressed files or streams.
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The functions are only available if the corresponding algorithm is compiled into
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the OpenSSL library. \s-1NULL\s0 may be returned if the algorithm fails to load dynamically.
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.SH "NOTES"
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.IX Header "NOTES"
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While compressing non-compressible data, the output may be larger than the
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input. Care should be taken to size output buffers appropriate for both
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compression and expansion.
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.PP
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Compression support and compression algorithms must be enabled and built into
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the library before use. Refer to the \s-1INSTALL\s0.md file when configuring OpenSSL.
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.PP
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\&\s-1ZLIB\s0 may be found at <https://zlib.net>
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.PP
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Brotli may be found at <https://github.com/google/brotli>.
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.PP
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Zstandard may be found at <https://github.com/facebook/zstd>.
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.PP
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Compression of \s-1SSL/TLS\s0 records is not recommended, as it has been
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shown to lead to the \s-1CRIME\s0 attack <https://en.wikipedia.org/wiki/CRIME>.
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It is disabled by default, and may be enabled by clearing the
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\&\s-1SSL_OP_NO_COMPRESSION\s0 option and setting the security level as appropriate.
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See the documentation for the \fISSL_CTX_set_options\fR\|(3) and
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\&\fISSL_set_options\fR\|(3) functions.
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.PP
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Compression is also used to support certificate compression as described
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in \s-1RFC8879 \s0<https://datatracker.ietf.org/doc/html/rfc8879>.
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It may be disabled via the \s-1SSL_OP_NO_TX_CERTIFICATE_COMPRESSION\s0 and
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\&\s-1SSL_OP_NO_RX_CERTIFICATE_COMPRESSION\s0 options of the
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\&\fISSL_CTX_set_options\fR\|(3) or \fISSL_set_options\fR\|(3) functions.
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.PP
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\&\fICOMP_zlib()\fR, \fICOMP_brotli()\fR and \fICOMP_zstd()\fR are stream-based compression methods.
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Internal state (including compression dictionary) is maintained between calls.
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If an error is returned, the stream is corrupted, and should be closed.
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.PP
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\&\fICOMP_zlib_oneshot()\fR, \fICOMP_brotli_oneshot()\fR and \fICOMP_zstd_oneshot()\fR are not stream-based. These
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methods do not maintain state between calls. An error in one call does not affect
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future calls.
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.SH "RETURN VALUES"
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.IX Header "RETURN VALUES"
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\&\fICOMP_CTX_new()\fR returns a \fB\s-1COMP_CTX\s0\fR on success, or \s-1NULL\s0 on failure.
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.PP
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\&\fICOMP_CTX_get_method()\fR, \fICOMP_zlib()\fR, \fICOMP_zlib_oneshot()\fR, \fICOMP_brotli()\fR, \fICOMP_brotli_oneshot()\fR,
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\&\fICOMP_zstd()\fR, and \fICOMP_zstd_oneshot()\fR return a \fB\s-1COMP_METHOD\s0\fR on success,
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or \s-1NULL\s0 on failure.
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.PP
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\&\fICOMP_CTX_get_type()\fR and \fICOMP_get_type()\fR return a \s-1NID\s0 value. On failure,
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NID_undef is returned.
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.PP
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\&\fICOMP_compress_block()\fR and \fICOMP_expand_block()\fR return the number of
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bytes stored in the output buffer \fIout\fR. This may be 0. On failure,
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\&\-1 is returned.
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.PP
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\&\fICOMP_get_name()\fR returns a \fBconst char *\fR that must not be freed
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on success, or \s-1NULL\s0 on failure.
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.PP
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\&\fIBIO_f_zlib()\fR, \fIBIO_f_brotli()\fR and \fIBIO_f_zstd()\fR return \s-1NULL\s0 on error, and
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a \fB\s-1BIO_METHOD\s0\fR on success.
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.SH "SEE ALSO"
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.IX Header "SEE ALSO"
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\&\fIBIO_new\fR\|(3), \fISSL_CTX_set_options\fR\|(3), \fISSL_set_options\fR\|(3)
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.SH "HISTORY"
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.IX Header "HISTORY"
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Brotli and Zstandard functions were added in OpenSSL 3.2.
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.SH "COPYRIGHT"
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.IX Header "COPYRIGHT"
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Copyright 2022 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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