There are fourteen operation options that set the type of operation to be
performed. The meaning of the other options varies according to the operation
type.
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. The
actual CMS type is <B>EnvelopedData<B>.
Note that no revocation check is done for the recipient cert, so if that
key has been compromised, others may be able to decrypt the text.
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 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.
Uncompress a CMS CompressedData type and output the content. OpenSSL must be
compiled with zlib support for this option to work, otherwise it will
output an error.
Generate and output a signed receipt for the supplied message. The input
message must contain a signed receipt request. Functionality is otherwise
similar to the -sign operation.
Verify a signed receipt in filename receipt. The input message must
contain the original receipt request. Functionality is otherwise similar
to the -verify operation.
This specifies the input format for the CMS structure. The default
is SMIME which reads an S/MIME format message. PEM and DER
format change this to expect PEM and DER format CMS structures
instead. This currently only affects the input format of the CMS
structure, if no CMS structure is being input (for example with
-encrypt or -sign) this option has no effect.
This specifies the output format for the CMS structure. The default
is SMIME which writes an S/MIME format message. PEM and DER
format change this to write PEM and DER format CMS structures
instead. This currently only affects the output format of the CMS
structure, if no CMS structure is being output (for example with
-verify or -decrypt) this option has no effect.
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.
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.
This specifies a file containing the detached content, this is only
useful with the -verify command. This is only usable if the CMS
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.
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.
For the -cmsout operation do not output the parsed CMS structure. This
is useful when combined with the -print option or if the syntax of the CMS
structure is being checked.
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.
The encryption algorithm to use. For example triple DES (168 bits) - -des3
or 256 bit AES - -aes256. Any standard algorithm name (as used by the
EVP_get_cipherbyname() function) can also be used preceded by a dash, for
example -aes-128-cbc. See enc(1) for a list of ciphers
supported by your version of OpenSSL.
If not specified triple DES is used. Only used with -encrypt and
-EncryptedData_create commands.
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.
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).
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.
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.
When signing use ASCII CRLF format canonicalisation. This strips trailing
whitespace from all lines, deletes trailing blank lines at EOF and sets
the encapsulated content type. This option is normally used with detached
content and an output signature format of DER. This option is not normally
needed when verifying as it is enabled automatically if the encapsulated
content format is detected.
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.
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.
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.
When decrypting a message this specifies the recipients certificate. The
certificate must match one of the recipients of the message or an error
occurs.
When encrypting a message this option may be used multiple times to specify
each recipient. This form must be used if customised parameters are
required (for example to specify RSA-OAEP).
Only certificates carrying RSA, Diffie-Hellman or EC keys are supported by this
option.
Use subject key identifier to identify certificates instead of issuer name and
serial number. The supplied certificate must include a subject key
identifier extension. Supported by -sign and -encrypt options.
For -sign option include a signed receipt request. Indicate requests should
be provided by all recipient or first tier recipients (those mailed directly
and not from a mailing list). Ignored it -receipt_request_from is included.
Specify symmetric key to use. The key must be supplied in hex format and be
consistent with the algorithm used. Supported by the -EncryptedData_encrypt-EncryptedData_decrypt, -encrypt and -decrypt options. When used
with -encrypt or -decrypt the supplied key is used to wrap or unwrap the
content encryption key using an AES key in the KEKRecipientInfo type.
The key identifier for the supplied symmetric key for KEKRecipientInfo type.
This option must be present if the -secretkey option is used with
-encrypt. With -decrypt operations the id is used to locate the
relevant key if it is not supplied then an attempt is used to decrypt any
KEKRecipientInfo structures.
Set the encapsulated content type to type if not supplied the Data type
is used. The type argument can be any valid OID name in either text or
numerical format.
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.
For signing and encryption this option can be used multiple times to
set customised parameters for the preceding key or certificate. It can
currently be used to set RSA-PSS for signing, RSA-OAEP for encryption
or to modify default parameters for ECDH.
A file or files containing random data used to seed the random number
generator.
Multiple files can be specified separated by an OS-dependent character.
The separator is ; for MS-Windows, , for OpenVMS, and : for
all others.
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.
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 won't 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 CMS enveloped data: CMS
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 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 CMS structure the encoding
remains DER.
If the -decrypt option is used without a recipient certificate then an
attempt is made to locate the recipient by trying each potential recipient
in turn using the supplied private key. To thwart the MMA attack
(Bleichenbacher's attack on PKCS #1 v1.5 RSA padding) all recipients are
tried whether they succeed or not and if no recipients match the message
is "decrypted" using a random key which will typically output garbage.
The -debug_decrypt option can be used to disable the MMA attack protection
and return an error if no recipient can be found: this option should be used
with caution. For a fuller description see CMS_decrypt(3)).
The smime utility can only process the older PKCS#7 format. The cms
utility supports Cryptographic Message Syntax format. Use of some features
will result in messages which cannot be processed by applications which only
support the older format. These are detailed below.
The use of the -keyid option with -sign or -encrypt.
The -outform PEM option uses different headers.
The -compress option.
The -secretkey option when used with -encrypt.
The use of PSS with -sign.
The use of OAEP or non-RSA keys with -encrypt.
Additionally the -EncryptedData_create and -data_create type cannot
be processed by the older smime command.
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:
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.
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Licensed under the OpenSSL license (the "License"). You may not use
this file except in compliance with the License. You can obtain a copy
in the file LICENSE in the source distribution or at
https://www.openssl.org/source/license.html.