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diff --git a/doc/info/libkeccak.texinfo b/doc/info/libkeccak.texinfo index b3516b3..c64c4b6 100644 --- a/doc/info/libkeccak.texinfo +++ b/doc/info/libkeccak.texinfo @@ -70,6 +70,7 @@ with support for bit-oriented data. * Overview:: Brief overview of libkeccak. * Linking:: How to use libkeccak in your software. * Selecting hash function:: Selecting and tuning the function. +* State of the hashing:: The structure used to keep track of the hashing process. * GNU Affero General Public License:: Copying and sharing libkeccak. * GNU Free Documentation License:: Copying and sharing this manual. @@ -305,6 +306,136 @@ returned: +@node State of the hashing +@chapter State of the hashing + +Hashing of a message is done by feeding segments of the +message to functions until all of the message has been +processed, and than the users may repeat the last phase +any number of times. Because functions are called multiple +times, the state of the process need to be stored in +a state structure. The structure used in libkeccak to +keep track of the state is called @code{libkeccak_state_t} +(@code{struct libkeccak_state}). + +Before you can use the functions for hashing a message, +you must allocate a state and initialise it. +To initialise a state, use the function +@code{libkeccak_state_initialise}. Its first argument +should be a pointer to the state variable, that is, +a @code{libkeccak_state_t*}. The second argument should +be a pointer to the specifications, that is, a +@code{const libkeccak_spec_t*}, see @ref{Selecting hash function}. +@code{libkeccak_state_initialise} till return zero +upon successful completion, and otherwise set +@code{errno} to describe the error and return @code{-1}. + +Once done with a state structure, you should release +allocated resources that are stored in the structure. +This can be done either by calling the function +@code{libkeccak_state_destroy} or by calling the function +@code{libkeccak_state_fast_destroy}. These two functions +are almost identical, both takes a pointer to the +state as its only parameter, and neither return a value. +However, @code{libkeccak_state_fast_destroy} will only +release allocations used by the state; @code{libkeccak_state_destroy} +will also securely release all sensitive information +in the state, by calling the function @code{libkeccak_state_wipe}: +the state of the sponge, by calling the function +@code{libkeccak_state_wipe_sponge}, and the message +buffer, by calling the function @code{libkeccak_state_wipe_message}. +@code{libkeccak_state_wipe}, @code{libkeccak_state_wipe_sponge} +and @code{libkeccak_state_wipe_message} takes a +pointer to the state as their only parameter, and +none of them have a return value. + +An alternative to destroying a state, you can reset +it if you want to reuse it to hash another message +using the same hashing function specifications. +This is done by calling @code{libkeccak_state_reset} +instead of @code{libkeccak_state_fast_destroy}. +It takes a pointer to the state as its only parameter +and does not return a value. + +If you want to use dynamic instead of static allocation +for the state, instead of calling @code{malloc} and +@code{free} yourself, libkeccak offers functions that +does this for you: +@table @code +@item libkeccak_state_create +Identical to @code{libkeccak_state_initialise}, except +it does have the first parameter, but it has the second +parameter (the specifications). It returns a pointer +to the allocate state upon successful completion, and +returns @code{NULL} on error, in which case, @code{errno} +is set to describe the error. + +@item libkeccak_state_fast_free +Identical to @code{libkeccak_state_fast_destroy}, except +it also frees the allocation of the state. + +@item libkeccak_state_free +Identical to @code{libkeccak_state_destroy}, except +it also frees the allocation of the state. +@end table + +libkeccak also has two functions for copying a state: +@table @code +@item libkeccak_state_copy +Takes an output pointer to a state as its first parameter, +and a pointer to the state to copy as its second parameter. +The content of the second parameter will be duplicated into +the first parameter. The state passed in the first parameter +must not be initialised, lest you will suffer a memory leak. +The function returns zero upon successful completion, and +on error, sets @code{errno} to describe the error and returns +@code{-1}. + +@item libkeccak_state_duplicate +Identical to @code{libkeccak_state_copy}, except it only +has one parameter, a pointer to the state to copy, and +returns a pointer to a state it has allocated and copied +the state to. On error, @code{errno} is set to describe the +error and @code{NULL} is returned. +@end table + +The library also offers functions for marshalling a state, +which can be useful when implementing programs that can +reexecuted into updated version of itself. +@table @code +@item libkeccak_state_marshal_size +Takes a pointer to a state to marshal as its only parameter, +and returns the number of bytes required to marshal it. + +@item libkeccak_state_marshal +Takes a pointer to a state to marshal as its first parameter, +and the buffer, to where the state shall be marshalled, as +its second parameter. The function will marshal the state +into the buffer and return the number of bytes written, +which will be the same as @code{libkeccak_state_marshal_size} +returns for the state. + +@item libkeccak_state_unmarshal +Takes an output pointer for the unmarshalled state as its +first parameter, and the buffer where the state is marshalled +as its second parameter. The function will unmarshal the +state from the buffer and store it into the pointer passed +to the first parameter. The function will then return the +number of read bytes, which will be the same as +@code{libkeccak_state_marshal_size} and @code{libkeccak_state_marshal} +returned for the state when it was marshalled, as what they +will return if called again with the unmarshalled function. +On error, @code{errno} is set to describe the error and zero +is returned. + +@item libkeccak_state_unmarshal_skip +Figures out how many bytes the marshalled state uses, +so that the buffers pointer can be incremented with +this value to skip pass the marshalled state. +@end table + + + @node GNU Affero General Public License @appendix GNU Affero General Public License @include agpl-3.0.texinfo |