digest-final

Arguments: context &key return

You may need to evaluate (require :digest) to load the digest code before calling this function.

Compute and return the hash from context, in a format determined by the return keyword argument. digest-init returns a context (and you specify the hashing type in that call).

return can be one of the following values:

• :integer (the default): the return value is an integer (typically a large integer) representing the digest. Warning: note that an integer representation of the digest potentially loses information if the generated signature has leading octet(s) containing only zeroes. Care should be taking when using this return type if you intend to further encode the signature (such as to a base64-encoded string). See the example below.
• :usb8: return an usb-8 array containing the digest.
• :hex: return a string containing the hexadecimal representation of the digest. See hex-string-to-integer.

cl-user(4): (setq c (digest-init 'md5))
#(1 35 69 103 137 171 205 239 254 220 ...)
cl-user(5): (digest-update c "foo")
cl-user(6): (digest-final c :return :usb8)
#(172 189 24 219 76 194 248 92 237 239 ...)

;;  Potential problem with :return :integer (or :return unspecified
;;  as the default is :integer). The call is to DIGEST-FILE which calls
;;  DIGEST-FINAL and returns the value MD5-FINAL returns.
;;
;;  Here we get the md5 value in a shell:
%  openssl dgst -md5 -hex cmp05-optdialog.jpg
MD5(cmp05-optdialog.jpg)= 03c6f3f0ede5188ac49c30e11e7afa4e

;; Now we get it with DIGEST-FILE:
cl-user(17): (digest-file 'md5 "~/cmp05-optdialog.jpg")
5020706479262241505478555770059160142
cl-user(18): (format t "~x" *)
3c6f3f0ede5188ac49c30e11e7afa4e
nil
cl-user(19): 

;; Note the hex values are the same but the leading 0 is not printed
;; by Lisp, which is dealing with the value as an integer. The leading
;; 0 is preserved when the :return is :hex:
cl-user(21): (digest-file 'md5 "~/cmp05-optdialog.jpg" :return :hex)
"03c6f3f0ede5188ac49c30e11e7afa4e"
cl-user(22): 

See MD*, SHA*, HMAC, and other message digest support in miscellaneous.htm.

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This page is new in the 9.0 release.
Created 2019.8.20.