324 lines
9.2 KiB
Text
324 lines
9.2 KiB
Text
=pod
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=head1 NAME
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EVP_MD_CTX_new, EVP_MD_CTX_reset, EVP_MD_CTX_free, EVP_MD_CTX_copy_ex,
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EVP_MD_CTX_ctrl, EVP_DigestInit_ex, EVP_DigestInit, EVP_DigestUpdate,
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EVP_DigestFinal_ex, EVP_DigestFinalXOF, EVP_DigestFinal,
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EVP_MD_CTX_copy, EVP_MD_type, EVP_MD_pkey_type, EVP_MD_size,
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EVP_MD_block_size, EVP_MD_CTX_md, EVP_MD_CTX_size,
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EVP_MD_CTX_block_size, EVP_MD_CTX_type, EVP_md_null,
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EVP_get_digestbyname, EVP_get_digestbynid,
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EVP_get_digestbyobj - EVP digest routines
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=head1 SYNOPSIS
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#include <openssl/evp.h>
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EVP_MD_CTX *EVP_MD_CTX_new(void);
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int EVP_MD_CTX_reset(EVP_MD_CTX *ctx);
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void EVP_MD_CTX_free(EVP_MD_CTX *ctx);
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void EVP_MD_CTX_ctrl(EVP_MD_CTX *ctx, int cmd, int p1, void* p2);
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int EVP_DigestInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);
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int EVP_DigestUpdate(EVP_MD_CTX *ctx, const void *d, size_t cnt);
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int EVP_DigestFinal_ex(EVP_MD_CTX *ctx, unsigned char *md, unsigned int *s);
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int EVP_DigestFinalXOF(EVP_MD_CTX *ctx, unsigned char *md, size_t len);
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int EVP_MD_CTX_copy_ex(EVP_MD_CTX *out, const EVP_MD_CTX *in);
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int EVP_DigestInit(EVP_MD_CTX *ctx, const EVP_MD *type);
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int EVP_DigestFinal(EVP_MD_CTX *ctx, unsigned char *md, unsigned int *s);
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int EVP_MD_CTX_copy(EVP_MD_CTX *out, EVP_MD_CTX *in);
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int EVP_MD_type(const EVP_MD *md);
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int EVP_MD_pkey_type(const EVP_MD *md);
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int EVP_MD_size(const EVP_MD *md);
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int EVP_MD_block_size(const EVP_MD *md);
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const EVP_MD *EVP_MD_CTX_md(const EVP_MD_CTX *ctx);
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int EVP_MD_CTX_size(const EVP_MD *ctx);
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int EVP_MD_CTX_block_size(const EVP_MD *ctx);
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int EVP_MD_CTX_type(const EVP_MD *ctx);
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const EVP_MD *EVP_md_null(void);
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const EVP_MD *EVP_get_digestbyname(const char *name);
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const EVP_MD *EVP_get_digestbynid(int type);
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const EVP_MD *EVP_get_digestbyobj(const ASN1_OBJECT *o);
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=head1 DESCRIPTION
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The EVP digest routines are a high level interface to message digests,
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and should be used instead of the cipher-specific functions.
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=over 4
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=item EVP_MD_CTX_new()
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Allocates and returns a digest context.
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=item EVP_MD_CTX_reset()
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Resets the digest context B<ctx>. This can be used to reuse an already
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existing context.
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=item EVP_MD_CTX_free()
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Cleans up digest context B<ctx> and frees up the space allocated to it.
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=item EVP_MD_CTX_ctrl()
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Performs digest-specific control actions on context B<ctx>.
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=item EVP_DigestInit_ex()
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Sets up digest context B<ctx> to use a digest B<type> from ENGINE B<impl>.
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B<type> will typically be supplied by a function such as EVP_sha1(). If
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B<impl> is NULL then the default implementation of digest B<type> is used.
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=item EVP_DigestUpdate()
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Hashes B<cnt> bytes of data at B<d> into the digest context B<ctx>. This
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function can be called several times on the same B<ctx> to hash additional
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data.
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=item EVP_DigestFinal_ex()
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Retrieves the digest value from B<ctx> and places it in B<md>. If the B<s>
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parameter is not NULL then the number of bytes of data written (i.e. the
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length of the digest) will be written to the integer at B<s>, at most
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B<EVP_MAX_MD_SIZE> bytes will be written. After calling EVP_DigestFinal_ex()
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no additional calls to EVP_DigestUpdate() can be made, but
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EVP_DigestInit_ex() can be called to initialize a new digest operation.
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=item EVP_DigestFinalXOF()
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Interfaces to extendable-output functions, XOFs, such as SHAKE128 and SHAKE256.
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It retrieves the digest value from B<ctx> and places it in B<len>-sized <B>md.
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After calling this function no additional calls to EVP_DigestUpdate() can be
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made, but EVP_DigestInit_ex() can be called to initialize a new operation.
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=item EVP_MD_CTX_copy_ex()
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Can be used to copy the message digest state from B<in> to B<out>. This is
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useful if large amounts of data are to be hashed which only differ in the last
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few bytes.
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=item EVP_DigestInit()
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Behaves in the same way as EVP_DigestInit_ex() except it always uses the
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default digest implementation.
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=item EVP_DigestFinal()
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Similar to EVP_DigestFinal_ex() except the digest context B<ctx> is
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automatically cleaned up.
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=item EVP_MD_CTX_copy()
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Similar to EVP_MD_CTX_copy_ex() except the destination B<out> does not have to
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be initialized.
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=item EVP_MD_size(),
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EVP_MD_CTX_size()
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Return the size of the message digest when passed an B<EVP_MD> or an
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B<EVP_MD_CTX> structure, i.e. the size of the hash.
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=item EVP_MD_block_size(),
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EVP_MD_CTX_block_size()
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Return the block size of the message digest when passed an B<EVP_MD> or an
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B<EVP_MD_CTX> structure.
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=item EVP_MD_type(),
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EVP_MD_CTX_type()
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Return the NID of the OBJECT IDENTIFIER representing the given message digest
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when passed an B<EVP_MD> structure. For example, C<EVP_MD_type(EVP_sha1())>
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returns B<NID_sha1>. This function is normally used when setting ASN1 OIDs.
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=item EVP_MD_CTX_md()
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Returns the B<EVP_MD> structure corresponding to the passed B<EVP_MD_CTX>.
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=item EVP_MD_pkey_type()
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Returns the NID of the public key signing algorithm associated with this
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digest. For example EVP_sha1() is associated with RSA so this will return
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B<NID_sha1WithRSAEncryption>. Since digests and signature algorithms are no
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longer linked this function is only retained for compatibility reasons.
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=item EVP_md_null()
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A "null" message digest that does nothing: i.e. the hash it returns is of zero
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length.
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=item EVP_get_digestbyname(),
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EVP_get_digestbynid(),
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EVP_get_digestbyobj()
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Returns an B<EVP_MD> structure when passed a digest name, a digest B<NID> or an
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B<ASN1_OBJECT> structure respectively.
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=back
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=head1 RETURN VALUES
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=over 4
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=item EVP_DigestInit_ex(),
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EVP_DigestUpdate(),
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EVP_DigestFinal_ex()
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Returns 1 for
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success and 0 for failure.
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=item EVP_MD_CTX_ctrl()
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Returns 1 if successful or 0 for failure.
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=item EVP_MD_CTX_copy_ex()
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Returns 1 if successful or 0 for failure.
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=item EVP_MD_type(),
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EVP_MD_pkey_type(),
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EVP_MD_type()
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Returns the NID of the corresponding OBJECT IDENTIFIER or NID_undef if none
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exists.
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=item EVP_MD_size(),
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EVP_MD_block_size(),
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EVP_MD_CTX_size(),
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EVP_MD_CTX_block_size()
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Returns the digest or block size in bytes.
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=item EVP_md_null()
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Returns a pointer to the B<EVP_MD> structure of the "null" message digest.
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=item EVP_get_digestbyname(),
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EVP_get_digestbynid(),
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EVP_get_digestbyobj()
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Returns either an B<EVP_MD> structure or NULL if an error occurs.
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=back
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=head1 NOTES
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The B<EVP> interface to message digests should almost always be used in
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preference to the low level interfaces. This is because the code then becomes
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transparent to the digest used and much more flexible.
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New applications should use the SHA-2 (such as L<EVP_sha256(3)>) or the SHA-3
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digest algorithms (such as L<EVP_sha3_512>). The other digest algorithms are
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still in common use.
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For most applications the B<impl> parameter to EVP_DigestInit_ex() will be
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set to NULL to use the default digest implementation.
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The functions EVP_DigestInit(), EVP_DigestFinal() and EVP_MD_CTX_copy() are
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obsolete but are retained to maintain compatibility with existing code. New
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applications should use EVP_DigestInit_ex(), EVP_DigestFinal_ex() and
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EVP_MD_CTX_copy_ex() because they can efficiently reuse a digest context
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instead of initializing and cleaning it up on each call and allow non default
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implementations of digests to be specified.
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If digest contexts are not cleaned up after use
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memory leaks will occur.
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EVP_MD_CTX_size(), EVP_MD_CTX_block_size(), EVP_MD_CTX_type(),
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EVP_get_digestbynid() and EVP_get_digestbyobj() are defined as
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macros.
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EVP_MD_CTX_ctrl() sends commands to message digests for additional configuration
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or control.
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=head1 EXAMPLE
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This example digests the data "Test Message\n" and "Hello World\n", using the
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digest name passed on the command line.
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#include <stdio.h>
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#include <openssl/evp.h>
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main(int argc, char *argv[])
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{
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EVP_MD_CTX *mdctx;
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const EVP_MD *md;
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char mess1[] = "Test Message\n";
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char mess2[] = "Hello World\n";
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unsigned char md_value[EVP_MAX_MD_SIZE];
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int md_len, i;
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if (argv[1] == NULL) {
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printf("Usage: mdtest digestname\n");
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exit(1);
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}
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md = EVP_get_digestbyname(argv[1]);
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if (md == NULL) {
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printf("Unknown message digest %s\n", argv[1]);
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exit(1);
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}
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mdctx = EVP_MD_CTX_new();
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EVP_DigestInit_ex(mdctx, md, NULL);
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EVP_DigestUpdate(mdctx, mess1, strlen(mess1));
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EVP_DigestUpdate(mdctx, mess2, strlen(mess2));
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EVP_DigestFinal_ex(mdctx, md_value, &md_len);
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EVP_MD_CTX_free(mdctx);
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printf("Digest is: ");
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for (i = 0; i < md_len; i++)
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printf("%02x", md_value[i]);
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printf("\n");
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exit(0);
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}
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=head1 SEE ALSO
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L<dgst(1)>,
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L<evp(7)>
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The full list of digest algorithms are provided below.
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L<EVP_blake2b512(3)>,
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L<EVP_md2(3)>,
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L<EVP_md4(3)>,
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L<EVP_md5(3)>,
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L<EVP_mdc2(3)>,
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L<EVP_ripemd160(3)>,
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L<EVP_sha1(3)>,
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L<EVP_sha224(3)>,
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L<EVP_sha3_224(3)>,
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L<EVP_sm3(3)>,
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L<EVP_whirlpool(3)>
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=head1 HISTORY
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EVP_MD_CTX_create() and EVP_MD_CTX_destroy() were renamed to
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EVP_MD_CTX_new() and EVP_MD_CTX_free() in OpenSSL 1.1.0.
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The link between digests and signing algorithms was fixed in OpenSSL 1.0 and
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later, so now EVP_sha1() can be used with RSA and DSA.
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EVP_dss1() was removed in OpenSSL 1.1.0.
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=head1 COPYRIGHT
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Copyright 2000-2018 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the OpenSSL license (the "License"). 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 LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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