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;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2013, 2014, 2015, 2017 Ludovic Courtès <ludo@gnu.org>
;;; This file is part of GNU Guix.
;;; GNU Guix is free software; you can redistribute it and/or modify it
;;; under the terms of the GNU General Public License as published by
;;; the Free Software Foundation; either version 3 of the License, or (at
;;; your option) any later version.
;;; GNU Guix is distributed in the hope that it will be useful, but
;;; WITHOUT ANY WARRANTY; without even the implied warranty of
;;; GNU General Public License for more details.
;;; You should have received a copy of the GNU General Public License
;;; along with GNU Guix. If not, see <http://www.gnu.org/licenses/>.
(define-module (guix pk-crypto)
#:use-module (guix base16)
#:use-module (guix gcrypt)
#:use-module (system foreign)
#:use-module (rnrs bytevectors)
#:use-module (ice-9 match)
#:use-module (ice-9 rdelim)
#:export (canonical-sexp?
#:re-export (gcrypt-version))
;;; Commentary:
;;; Public key cryptographic routines from GNU Libgcrypt.
;;; Libgcrypt uses "canonical s-expressions" to represent key material,
;;; parameters, and data. We keep it as an opaque object to map them to
;;; Scheme s-expressions because (1) Libgcrypt sexps may be stored in secure
;;; memory, and (2) the read syntax is different.
;;; A 'canonical-sexp->sexp' procedure is provided nevertheless, for use in
;;; cases where it is safe to move data out of Libgcrypt---e.g., when
;;; processing ACL entries, public keys, etc.
;;; Canonical sexps were defined by Rivest et al. in the IETF draft at
;;; <http://people.csail.mit.edu/rivest/Sexp.txt> for the purposes of SPKI
;;; (see <http://www.ietf.org/rfc/rfc2693.txt>.)
;;; Code:
;; Libgcrypt "s-expressions".
(define-wrapped-pointer-type <canonical-sexp>
(lambda (obj port)
;; Don't print OBJ's external representation: we don't want key material
;; to leak in backtraces and such.
(format port "#<canonical-sexp ~a | ~a>"
(number->string (object-address obj) 16)
(number->string (pointer-address (canonical-sexp->pointer obj))
(define finalize-canonical-sexp!
(libgcrypt-func "gcry_sexp_release"))
(define-inlinable (pointer->canonical-sexp ptr)
"Return a <canonical-sexp> that wraps PTR."
(let* ((sexp (naked-pointer->canonical-sexp ptr))
(ptr* (canonical-sexp->pointer sexp)))
;; Did we already have a <canonical-sexp> object for PTR?
(when (equal? ptr ptr*)
;; No, so we can safely add a finalizer (in Guile 2.0.9
;; 'set-pointer-finalizer!' *adds* a finalizer rather than replacing the
;; existing one.)
(set-pointer-finalizer! ptr finalize-canonical-sexp!))
(define error-source
(let* ((ptr (libgcrypt-func "gcry_strsource"))
(proc (pointer->procedure '* ptr (list int))))
(lambda (err)
"Return the error source (a string) for ERR, an error code as thrown
along with 'gcry-error'."
(pointer->string (proc err)))))
(define error-string
(let* ((ptr (libgcrypt-func "gcry_strerror"))
(proc (pointer->procedure '* ptr (list int))))
(lambda (err)
"Return the error description (a string) for ERR, an error code as
thrown along with 'gcry-error'."
(pointer->string (proc err)))))
(define string->canonical-sexp
(let* ((ptr (libgcrypt-func "gcry_sexp_new"))
(proc (pointer->procedure int ptr `(* * ,size_t ,int))))
(lambda (str)
"Parse STR and return the corresponding gcrypt s-expression."
;; When STR comes from 'canonical-sexp->string', it may contain
;; characters that are really meant to be interpreted as bytes as in a C
;; 'char *'. Thus, convert STR to ISO-8859-1 so the byte values of the
;; characters are preserved.
(let* ((sexp (bytevector->pointer (make-bytevector (sizeof '*))))
(err (proc sexp (string->pointer str "ISO-8859-1") 0 1)))
(if (= 0 err)
(pointer->canonical-sexp (dereference-pointer sexp))
(throw 'gcry-error 'string->canonical-sexp err))))))
(identifier-syntax 3))
(define canonical-sexp->string
(let* ((ptr (libgcrypt-func "gcry_sexp_sprint"))
(proc (pointer->procedure size_t ptr `(* ,int * ,size_t))))
(lambda (sexp)
"Return a textual representation of SEXP."
(let loop ((len 1024))
(let* ((buf (bytevector->pointer (make-bytevector len)))
(size (proc (canonical-sexp->pointer sexp)
(if (zero? size)
(loop (* len 2))
(pointer->string buf size "ISO-8859-1")))))))
(define (read-file-sexp file)
"Return the canonical sexp read from FILE."
(call-with-input-file file
(compose string->canonical-sexp
(define canonical-sexp-car
(let* ((ptr (libgcrypt-func "gcry_sexp_car"))
(proc (pointer->procedure '* ptr '(*))))
(lambda (lst)
"Return the first element of LST, an sexp, if that element is a list;
return #f if LST or its first element is not a list (this is different from
the usual Lisp 'car'.)"
(let ((result (proc (canonical-sexp->pointer lst))))
(if (null-pointer? result)
(pointer->canonical-sexp result))))))
(define canonical-sexp-cdr
(let* ((ptr (libgcrypt-func "gcry_sexp_cdr"))
(proc (pointer->procedure '* ptr '(*))))
(lambda (lst)
"Return the tail of LST, an sexp, or #f if LST is not a list."
(let ((result (proc (canonical-sexp->pointer lst))))
(if (null-pointer? result)
(pointer->canonical-sexp result))))))
(define canonical-sexp-nth
(let* ((ptr (libgcrypt-func "gcry_sexp_nth"))
(proc (pointer->procedure '* ptr `(* ,int))))
(lambda (lst index)
"Return the INDEXth nested element of LST, an s-expression. Return #f
if that element does not exist, or if it's an atom. (Note: this is obviously
different from Scheme's 'list-ref'.)"
(let ((result (proc (canonical-sexp->pointer lst) index)))
(if (null-pointer? result)
(pointer->canonical-sexp result))))))
(define (dereference-size_t p)
"Return the size_t value pointed to by P."
(bytevector-uint-ref (pointer->bytevector p (sizeof size_t))
0 (native-endianness)
(sizeof size_t)))
(define canonical-sexp-length
(let* ((ptr (libgcrypt-func "gcry_sexp_length"))
(proc (pointer->procedure int ptr '(*))))
(lambda (sexp)
"Return the length of SEXP if it's a list (including the empty list);
return zero if SEXP is an atom."
(proc (canonical-sexp->pointer sexp)))))
(define token-string?
(let ((token-cs (char-set-union char-set:digit
(char-set #\- #\. #\/ #\_
#\: #\* #\+ #\=))))
(lambda (str)
"Return #t if STR is a token as per Section 4.3 of
(and (not (string-null? str))
(string-every token-cs str)
(not (char-set-contains? char-set:digit (string-ref str 0)))))))
(define canonical-sexp-nth-data
(let* ((ptr (libgcrypt-func "gcry_sexp_nth_data"))
(proc (pointer->procedure '* ptr `(* ,int *))))
(lambda (lst index)
"Return as a symbol (for \"sexp tokens\") or a bytevector (for any other
\"octet string\") the INDEXth data element (atom) of LST, an s-expression.
Return #f if that element does not exist, or if it's a list."
(let* ((size* (bytevector->pointer (make-bytevector (sizeof '*))))
(result (proc (canonical-sexp->pointer lst) index size*)))
(if (null-pointer? result)
(let* ((len (dereference-size_t size*))
(str (pointer->string result len "ISO-8859-1")))
;; The sexp spec speaks of "tokens" and "octet strings".
;; Sometimes these octet strings are actual strings (text),
;; sometimes they're bytevectors, and sometimes they're
;; multi-precision integers (MPIs). Only the application knows.
;; However, for convenience, we return a symbol when a token is
;; encountered since tokens are frequent (at least in the 'car'
;; of each sexp.)
(if (token-string? str)
(string->symbol str) ; an sexp "token"
(bytevector-copy ; application data, textual or binary
(pointer->bytevector result len)))))))))
(define (number->canonical-sexp number)
"Return an s-expression representing NUMBER."
(string->canonical-sexp (string-append "#" (number->string number 16) "#")))
(define* (bytevector->hash-data bv
(hash-algo "sha256")
#:key (key-type 'ecc))
"Given BV, a bytevector containing a hash of type HASH-ALGO, return an
s-expression suitable for use as the 'data' argument for 'sign'. KEY-TYPE
must be a symbol: 'dsa, 'ecc, or 'rsa."
(format #f "(data (flags ~a) (hash \"~a\" #~a#))"
(case key-type
((ecc dsa) "rfc6979")
((rsa) "pkcs1")
(else (error "unknown key type" key-type)))
(bytevector->base16-string bv))))
(define (key-type sexp)
"Return a symbol denoting the type of public or private key represented by
SEXP--e.g., 'rsa', 'ecc'--or #f if SEXP does not denote a valid key."
(case (canonical-sexp-nth-data sexp 0)
((public-key private-key)
(canonical-sexp-nth-data (canonical-sexp-nth sexp 1) 0))
(else #f)))
(define* (hash-data->bytevector data)
"Return two values: the hash value (a bytevector), and the hash algorithm (a
string) extracted from DATA, an sexp as returned by 'bytevector->hash-data'.
Return #f if DATA does not conform."
(let ((hash (find-sexp-token data 'hash)))
(if hash
(let ((algo (canonical-sexp-nth-data hash 1))
(value (canonical-sexp-nth-data hash 2)))
(values value (symbol->string algo)))
(values #f #f))))
(define sign
(let* ((ptr (libgcrypt-func "gcry_pk_sign"))
(proc (pointer->procedure int ptr '(* * *))))
(lambda (data secret-key)
"Sign DATA, a canonical s-expression representing a suitable hash, with
SECRET-KEY (a canonical s-expression whose car is 'private-key'.) Note that
DATA must be a 'data' s-expression, as returned by
'bytevector->hash-data' (info \"(gcrypt) Cryptographic Functions\")."
(let* ((sig (bytevector->pointer (make-bytevector (sizeof '*))))
(err (proc sig (canonical-sexp->pointer data)
(canonical-sexp->pointer secret-key))))
(if (= 0 err)
(pointer->canonical-sexp (dereference-pointer sig))
(throw 'gcry-error 'sign err))))))
(define verify
(let* ((ptr (libgcrypt-func "gcry_pk_verify"))
(proc (pointer->procedure int ptr '(* * *))))
(lambda (signature data public-key)
"Verify that SIGNATURE is a signature of DATA with PUBLIC-KEY, all of
which are gcrypt s-expressions."
(zero? (proc (canonical-sexp->pointer signature)
(canonical-sexp->pointer data)
(canonical-sexp->pointer public-key))))))
(define generate-key
(let* ((ptr (libgcrypt-func "gcry_pk_genkey"))
(proc (pointer->procedure int ptr '(* *))))
(lambda (params)
"Return as an s-expression a new key pair for PARAMS. PARAMS must be an
s-expression like: (genkey (rsa (nbits 4:2048)))."
(let* ((key (bytevector->pointer (make-bytevector (sizeof '*))))
(err (proc key (canonical-sexp->pointer params))))
(if (zero? err)
(pointer->canonical-sexp (dereference-pointer key))
(throw 'gcry-error 'generate-key err))))))
(define find-sexp-token
(let* ((ptr (libgcrypt-func "gcry_sexp_find_token"))
(proc (pointer->procedure '* ptr `(* * ,size_t))))
(lambda (sexp token)
"Find in SEXP the first element whose 'car' is TOKEN and return it;
return #f if not found."
(let* ((token (string->pointer (symbol->string token)))
(res (proc (canonical-sexp->pointer sexp) token 0)))
(if (null-pointer? res)
(pointer->canonical-sexp res))))))
(define-inlinable (canonical-sexp-null? sexp)
"Return #t if SEXP is the empty-list sexp."
(null-pointer? (canonical-sexp->pointer sexp)))
(define (canonical-sexp-list? sexp)
"Return #t if SEXP is a list."
(or (canonical-sexp-null? sexp)
(> (canonical-sexp-length sexp) 0)))
(define (canonical-sexp-fold proc seed sexp)
"Fold PROC (as per SRFI-1) over SEXP, a canonical sexp."
(if (canonical-sexp-list? sexp)
(let ((len (canonical-sexp-length sexp)))
(let loop ((index 0)
(result seed))
(if (= index len)
(loop (+ 1 index)
;; XXX: Call 'nth-data' *before* 'nth' to work around
;; <https://bugs.g10code.com/gnupg/issue1594>, which
;; affects 1.6.0 and earlier versions.
(proc (or (canonical-sexp-nth-data sexp index)
(canonical-sexp-nth sexp index))
(error "sexp is not a list" sexp)))
(define (canonical-sexp->sexp sexp)
"Return a Scheme sexp corresponding to SEXP. This is particularly useful to
compare sexps (since Libgcrypt does not provide an 'equal?' procedure), or to
use pattern matching."
(if (canonical-sexp-list? sexp)
(canonical-sexp-fold (lambda (item result)
(cons (if (canonical-sexp? item)
(canonical-sexp->sexp item)
;; As of Libgcrypt 1.6.0, there's no function to extract the buffer of a
;; non-list sexp (!), so we first enlist SEXP, then get at its buffer.
(let ((sexp (string->canonical-sexp
(string-append "(" (canonical-sexp->string sexp)
(or (canonical-sexp-nth-data sexp 0)
(canonical-sexp-nth sexp 0)))))
(define (sexp->canonical-sexp sexp)
"Return a canonical sexp equivalent to SEXP, a Scheme sexp as returned by
;; XXX: This is inefficient, but the Libgcrypt API doesn't allow us to do
;; much better.
(lambda (port)
(define (write item)
(cond ((list? item)
(display "(" port)
(for-each write item)
(display ")" port))
((symbol? item)
(format port " ~a" item))
((bytevector? item)
(format port " #~a#"
(bytevector->base16-string item)))
(error "unsupported sexp item type" item))))
(write sexp)))))
(define (gcrypt-error-printer port key args default-printer)
"Print the gcrypt error specified by ARGS."
(match args
((proc err)
(format port "In procedure ~a: ~a: ~a"
proc (error-source err) (error-string err)))))
(set-exception-printer! 'gcry-error gcrypt-error-printer)
;;; pk-crypto.scm ends here