SMIME(1ssl)
NAME
smime - S/MIME utility
SYNOPSIS
openssl smime [-encrypt] [-decrypt] [-sign] [-verify] [-pk7out] [-des] [-des3] [-rc2-40] [-rc2-64] [-rc2-128] [-aes128] [-aes192] [-aes256] [-camellia128] [-camellia192] [-camellia256] [-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] [-rand file(s)] [cert.pem]...
DESCRIPTION
The smime command handles S/MIME mail. It can encrypt, decrypt, sign
and verify S/MIME messages.
COMMAND OPTIONS
There are five 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. - -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. - -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. - -des -des3 -rc2-40 -rc2-64 -rc2-128 -aes128 -aes192 -aes256 -camellia128 -camellia192 -camellia256
- the encryption algorithm to use. DES (56 bits), triple DES (168
bits), 40, 64 or 128 bit RC2, 128, 192 or 256 bit AES, or 128, 192 or 256 bit Camellia respectively. 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
- the signers certificate when signing a message. 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.
- -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.
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.
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 and 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- 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
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.