.\"	$NetBSD: krb5_create_checksum.3,v 1.2 2017/01/28 21:31:49 christos Exp $
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.Dd August 12, 2005
.Dt NAME 3
.Os
.Sh NAME
.Nm krb5_checksum ,
.Nm krb5_checksum_disable ,
.Nm krb5_checksum_is_collision_proof ,
.Nm krb5_checksum_is_keyed ,
.Nm krb5_checksumsize ,
.Nm krb5_cksumtype_valid ,
.Nm krb5_copy_checksum ,
.Nm krb5_create_checksum ,
.Nm krb5_crypto_get_checksum_type
.Nm krb5_free_checksum ,
.Nm krb5_free_checksum_contents ,
.Nm krb5_hmac ,
.Nm krb5_verify_checksum
.Nd creates, handles and verifies checksums
.Sh LIBRARY
Kerberos 5 Library (libkrb5, -lkrb5)
.Sh SYNOPSIS
.In krb5/krb5.h
.Pp
.Li "typedef Checksum krb5_checksum;"
.Ft void
.Fo krb5_checksum_disable
.Fa "krb5_context context"
.Fa "krb5_cksumtype type"
.Fc
.Ft krb5_boolean
.Fo krb5_checksum_is_collision_proof
.Fa "krb5_context context"
.Fa "krb5_cksumtype type"
.Fc
.Ft krb5_boolean
.Fo krb5_checksum_is_keyed
.Fa "krb5_context context"
.Fa "krb5_cksumtype type"
.Fc
.Ft krb5_error_code
.Fo krb5_cksumtype_valid
.Fa "krb5_context context"
.Fa "krb5_cksumtype ctype"
.Fc
.Ft krb5_error_code
.Fo krb5_checksumsize
.Fa "krb5_context context"
.Fa "krb5_cksumtype type"
.Fa "size_t *size"
.Fc
.Ft krb5_error_code
.Fo krb5_create_checksum
.Fa "krb5_context context"
.Fa "krb5_crypto crypto"
.Fa "krb5_key_usage usage"
.Fa "int type"
.Fa "void *data"
.Fa "size_t len"
.Fa "Checksum *result"
.Fc
.Ft krb5_error_code
.Fo krb5_verify_checksum
.Fa "krb5_context context"
.Fa "krb5_crypto crypto"
.Fa "krb5_key_usage usage"
.Fa "void *data"
.Fa "size_t len"
.Fa "Checksum *cksum"
.Fc
.Ft krb5_error_code
.Fo krb5_crypto_get_checksum_type
.Fa "krb5_context context"
.Fa "krb5_crypto crypto"
.Fa "krb5_cksumtype *type"
.Fc
.Ft void
.Fo krb5_free_checksum
.Fa "krb5_context context"
.Fa "krb5_checksum *cksum"
.Fc
.Ft void
.Fo krb5_free_checksum_contents
.Fa "krb5_context context"
.Fa "krb5_checksum *cksum"
.Fc
.Ft krb5_error_code
.Fo krb5_hmac
.Fa "krb5_context context"
.Fa "krb5_cksumtype cktype"
.Fa "const void *data"
.Fa "size_t len"
.Fa "unsigned usage"
.Fa "krb5_keyblock *key"
.Fa "Checksum *result"
.Fc
.Ft krb5_error_code
.Fo krb5_copy_checksum
.Fa "krb5_context context"
.Fa "const krb5_checksum *old"
.Fa "krb5_checksum **new"
.Fc
.Sh DESCRIPTION
The
.Li krb5_checksum
structure holds a Kerberos checksum.
There is no component inside
.Li krb5_checksum
that is directly referable.
.Pp
The functions are used to create and verify checksums.
.Fn krb5_create_checksum
creates a checksum of the specified data, and puts it in
.Fa result .
If
.Fa crypto
is
.Dv NULL ,
.Fa usage_or_type
specifies the checksum type to use; it must not be keyed. Otherwise
.Fa crypto
is an encryption context created by
.Fn krb5_crypto_init ,
and
.Fa usage_or_type
specifies a key-usage.
.Pp
.Fn krb5_verify_checksum
verifies the
.Fa checksum
against the provided data.
.Pp
.Fn krb5_checksum_is_collision_proof
returns true is the specified checksum is collision proof (that it's
very unlikely that two strings has the same hash value, and that it's
hard to find two strings that has the same hash). Examples of
collision proof checksums are MD5, and SHA1, while CRC32 is not.
.Pp
.Fn krb5_checksum_is_keyed
returns true if the specified checksum type is keyed (that the hash
value is a function of both the data, and a separate key). Examples of
keyed hash algorithms are HMAC-SHA1-DES3, and RSA-MD5-DES. The
.Dq plain
hash functions MD5, and SHA1 are not keyed.
.Pp
.Fn krb5_crypto_get_checksum_type
returns the checksum type that will be used when creating a checksum for the given
.Fa crypto
context.
This function is useful in combination with
.Fn krb5_checksumsize
when you want to know the size a checksum will
use when you create it.
.Pp
.Fn krb5_cksumtype_valid
returns 0 or an error if the checksumtype is implemented and not
currently disabled in this kerberos library.
.Pp
.Fn krb5_checksumsize
returns the size of the outdata of checksum function.
.Pp
.Fn krb5_copy_checksum
returns a copy of the checksum
.Fn krb5_free_checksum
should use used to free the
.Fa new
checksum.
.Pp
.Fn krb5_free_checksum
free the checksum and the content of the checksum.
.Pp
.Fn krb5_free_checksum_contents
frees the content of checksum in
.Fa cksum .
.Pp
.Fn krb5_hmac
calculates the HMAC over
.Fa data
(with length
.Fa len )
using the keyusage
.Fa usage
and keyblock
.Fa key .
Note that keyusage is not always used in checksums.
.Pp
.Nm krb5_checksum_disable
globally disables the checksum type.
.\" .Sh EXAMPLE
.\" .Sh BUGS
.Sh SEE ALSO
.Xr krb5_crypto_init 3 ,
.Xr krb5_c_encrypt 3 ,
.Xr krb5_encrypt 3