NAME¶
smime - S/MIME utility
SYNOPSIS¶
openssl smime [
-encrypt] [
-decrypt] [
-sign] [
-resign] [
-verify] [
-pk7out] [
-[cipher]] [
-in file] [
-certfile file] [
-signer
file] [
-recip file] [
-inform SMIME|PEM|DER] [
-passin
arg] [
-inkey file] [
-out file] [
-outform
SMIME|PEM|DER] [
-content file] [
-to addr] [
-from
ad] [
-subject s] [
-text] [
-indef] [
-noindef] [
-stream] [
-rand file(s)] [
-md
digest] [cert.pem]...
DESCRIPTION¶
The
smime command handles S/MIME mail. It can encrypt, decrypt, sign and
verify S/MIME messages.
COMMAND OPTIONS¶
There are six operation options that set the type of operation to be performed.
The meaning of the other options varies according to the operation type.
- -encrypt
- encrypt mail for the given recipient certificates. Input
file is the message to be encrypted. The output file is the encrypted mail
in MIME format.
- -decrypt
- decrypt mail using the supplied certificate and private
key. Expects an encrypted mail message in MIME format for the input file.
The decrypted mail is written to the output file.
- -sign
- sign mail using the supplied certificate and private key.
Input file is the message to be signed. The signed message in MIME format
is written to the output file.
- -verify
- verify signed mail. Expects a signed mail message on input
and outputs the signed data. Both clear text and opaque signing is
supported.
- -pk7out
- takes an input message and writes out a PEM encoded PKCS#7
structure.
- -resign
- resign a message: take an existing message and one or more
new signers.
- -in filename
- the input message to be encrypted or signed or the MIME
message to be decrypted or verified.
- -inform SMIME|PEM|DER
- this specifies the input format for the PKCS#7 structure.
The default is SMIME which reads an S/MIME format message.
PEM and DER format change this to expect PEM and DER format
PKCS#7 structures instead. This currently only affects the input format of
the PKCS#7 structure, if no PKCS#7 structure is being input (for example
with -encrypt or -sign) this option has no effect.
- -out filename
- the message text that has been decrypted or verified or the
output MIME format message that has been signed or verified.
- -outform SMIME|PEM|DER
- this specifies the output format for the PKCS#7 structure.
The default is SMIME which write an S/MIME format message.
PEM and DER format change this to write PEM and DER format
PKCS#7 structures instead. This currently only affects the output format
of the PKCS#7 structure, if no PKCS#7 structure is being output (for
example with -verify or -decrypt) this option has no
effect.
- -stream -indef -noindef
- the -stream and -indef options are equivalent
and enable streaming I/O for encoding operations. This permits single pass
processing of data without the need to hold the entire contents in memory,
potentially supporting very large files. Streaming is automatically set
for S/MIME signing with detached data if the output format is SMIME
it is currently off by default for all other operations.
- -noindef
- disable streaming I/O where it would produce and indefinite
length constructed encoding. This option currently has no effect. In
future streaming will be enabled by default on all relevant operations and
this option will disable it.
- -content filename
- This specifies a file containing the detached content, this
is only useful with the -verify command. This is only usable if the
PKCS#7 structure is using the detached signature form where the content is
not included. This option will override any content if the input format is
S/MIME and it uses the multipart/signed MIME content type.
- -text
- this option adds plain text (text/plain) MIME headers to
the supplied message if encrypting or signing. If decrypting or verifying
it strips off text headers: if the decrypted or verified message is not of
MIME type text/plain then an error occurs.
- -CAfile file
- a file containing trusted CA certificates, only used with
-verify.
- -CApath dir
- a directory containing trusted CA certificates, only used
with -verify. This directory must be a standard certificate
directory: that is a hash of each subject name (using x509 -hash)
should be linked to each certificate.
- -md digest
- digest algorithm to use when signing or resigning. If not
present then the default digest algorithm for the signing key will be used
(usually SHA1).
- -[cipher]
- the encryption algorithm to use. For example DES (56 bits)
- -des, triple DES (168 bits) - -des3,
EVP_get_cipherbyname() function) can also be used preceded by a
dash, for example -aes_128_cbc. See enc for list of ciphers
supported by your version of OpenSSL.
If not specified 40 bit RC2 is used. Only used with -encrypt.
- -nointern
- when verifying a message normally certificates (if any)
included in the message are searched for the signing certificate. With
this option only the certificates specified in the -certfile option
are used. The supplied certificates can still be used as untrusted CAs
however.
- -noverify
- do not verify the signers certificate of a signed
message.
- -nochain
- do not do chain verification of signers certificates: that
is don't use the certificates in the signed message as untrusted CAs.
- -nosigs
- don't try to verify the signatures on the message.
- -nocerts
- when signing a message the signer's certificate is normally
included with this option it is excluded. This will reduce the size of the
signed message but the verifier must have a copy of the signers
certificate available locally (passed using the -certfile option
for example).
- -noattr
- normally when a message is signed a set of attributes are
included which include the signing time and supported symmetric
algorithms. With this option they are not included.
- -binary
- normally the input message is converted to
"canonical" format which is effectively using CR and LF as end
of line: as required by the S/MIME specification. When this option is
present no translation occurs. This is useful when handling binary data
which may not be in MIME format.
- -nodetach
- when signing a message use opaque signing: this form is
more resistant to translation by mail relays but it cannot be read by mail
agents that do not support S/MIME. Without this option cleartext signing
with the MIME type multipart/signed is used.
- -certfile file
- allows additional certificates to be specified. When
signing these will be included with the message. When verifying these will
be searched for the signers certificates. The certificates should be in
PEM format.
- -signer file
- a signing certificate when signing or resigning a message,
this option can be used multiple times if more than one signer is
required. If a message is being verified then the signers certificates
will be written to this file if the verification was successful.
- -recip file
- the recipients certificate when decrypting a message. This
certificate must match one of the recipients of the message or an error
occurs.
- -inkey file
- the private key to use when signing or decrypting. This
must match the corresponding certificate. If this option is not specified
then the private key must be included in the certificate file specified
with the -recip or -signer file. When signing this option
can be used multiple times to specify successive keys.
- -passin arg
- the private key password source. For more information about
the format of arg see the PASS PHRASE ARGUMENTS section in
openssl(1).
- -rand file(s)
- a file or files containing random data used to seed the
random number generator, or an EGD socket (see RAND_egd(3)).
Multiple files can be specified separated by a OS-dependent character. The
separator is ; for MS-Windows, , for OpenVMS, and :
for all others.
- cert.pem...
- one or more certificates of message recipients: used when
encrypting a message.
- -to, -from, -subject
- the relevant mail headers. These are included outside the
signed portion of a message so they may be included manually. If signing
then many S/MIME mail clients check the signers certificate's email
address matches that specified in the From: address.
- -purpose, -ignore_critical, -issuer_checks, -crl_check,
-crl_check_all, -policy_check, -extended_crl, -x509_strict, -policy
-check_ss_sig
- Set various options of certificate chain verification. See
verify manual page for details.
NOTES¶
The MIME message must be sent without any blank lines between the headers and
the output. Some mail programs will automatically add a blank line. Piping the
mail directly to sendmail is one way to achieve the correct format.
The supplied message to be signed or encrypted must include the necessary MIME
headers or many S/MIME clients wont display it properly (if at all). You can
use the
-text option to automatically add plain text headers.
A "signed and encrypted" message is one where a signed message is then
encrypted. This can be produced by encrypting an already signed message: see
the examples section.
This version of the program only allows one signer per message but it will
verify multiple signers on received messages. Some S/MIME clients choke if a
message contains multiple signers. It is possible to sign messages "in
parallel" by signing an already signed message.
The options
-encrypt and
-decrypt reflect common usage in S/MIME
clients. Strictly speaking these process PKCS#7 enveloped data: PKCS#7
encrypted data is used for other purposes.
The
-resign option uses an existing message digest when adding a new
signer. This means that attributes must be present in at least one existing
signer using the same message digest or this operation will fail.
The
-stream and
-indef options enable experimental streaming I/O
support. As a result the encoding is BER using indefinite length constructed
encoding and no longer DER. Streaming is supported for the
-encrypt
operation and the
-sign operation if the content is not detached.
Streaming is always used for the
-sign operation with detached data but
since the content is no longer part of the PKCS#7 structure the encoding
remains DER.
EXIT CODES¶
- 0
- the operation was completely successfully.
- 1
- an error occurred parsing the command options.
- 2
- one of the input files could not be read.
- 3
- an error occurred creating the PKCS#7 file or when reading
the MIME message.
- 4
- an error occurred decrypting or verifying the message.
- 5
- the message was verified correctly but an error occurred
writing out the signers certificates.
EXAMPLES¶
Create a cleartext signed message:
openssl smime -sign -in message.txt -text -out mail.msg \
-signer mycert.pem
Create an opaque signed message:
openssl smime -sign -in message.txt -text -out mail.msg -nodetach \
-signer mycert.pem
Create a signed message, include some additional certificates and read the
private key from another file:
openssl smime -sign -in in.txt -text -out mail.msg \
-signer mycert.pem -inkey mykey.pem -certfile mycerts.pem
Create a signed message with two signers:
openssl smime -sign -in message.txt -text -out mail.msg \
-signer mycert.pem -signer othercert.pem
Send a signed message under Unix directly to sendmail, including headers:
openssl smime -sign -in in.txt -text -signer mycert.pem \
-from steve@openssl.org -to someone@somewhere \
-subject "Signed message" | sendmail someone@somewhere
Verify a message and extract the signer's certificate if successful:
openssl smime -verify -in mail.msg -signer user.pem -out signedtext.txt
Send encrypted mail using triple DES:
openssl smime -encrypt -in in.txt -from steve@openssl.org \
-to someone@somewhere -subject "Encrypted message" \
-des3 user.pem -out mail.msg
Sign and encrypt mail:
openssl smime -sign -in ml.txt -signer my.pem -text \
| openssl smime -encrypt -out mail.msg \
-from steve@openssl.org -to someone@somewhere \
-subject "Signed and Encrypted message" -des3 user.pem
Note: the encryption command does not include the
-text option because
the message being encrypted already has MIME headers.
Decrypt mail:
openssl smime -decrypt -in mail.msg -recip mycert.pem -inkey key.pem
The output from Netscape form signing is a PKCS#7 structure with the detached
signature format. You can use this program to verify the signature by line
wrapping the base64 encoded structure and surrounding it with:
-----BEGIN PKCS7-----
-----END PKCS7-----
and using the command:
openssl smime -verify -inform PEM -in signature.pem -content content.txt
Alternatively you can base64 decode the signature and use:
openssl smime -verify -inform DER -in signature.der -content content.txt
Create an encrypted message using 128 bit Camellia:
openssl smime -encrypt -in plain.txt -camellia128 -out mail.msg cert.pem
Add a signer to an existing message:
openssl smime -resign -in mail.msg -signer newsign.pem -out mail2.msg
BUGS¶
The MIME parser isn't very clever: it seems to handle most messages that I've
thrown at it but it may choke on others.
The code currently will only write out the signer's certificate to a file: if
the signer has a separate encryption certificate this must be manually
extracted. There should be some heuristic that determines the correct
encryption certificate.
Ideally a database should be maintained of a certificates for each email
address.
The code doesn't currently take note of the permitted symmetric encryption
algorithms as supplied in the SMIMECapabilities signed attribute. This means
the user has to manually include the correct encryption algorithm. It should
store the list of permitted ciphers in a database and only use those.
No revocation checking is done on the signer's certificate.
The current code can only handle S/MIME v2 messages, the more complex S/MIME v3
structures may cause parsing errors.
HISTORY¶
The use of multiple
-signer options and the
-resign command were
first added in OpenSSL 1.0.0