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450 lines
14 KiB
450 lines
14 KiB
=pod |
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=head1 NAME |
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smime - S/MIME utility |
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=head1 SYNOPSIS |
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B<openssl> B<smime> |
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[B<-encrypt>] |
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[B<-decrypt>] |
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[B<-sign>] |
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[B<-resign>] |
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[B<-verify>] |
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[B<-pk7out>] |
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[B<-[cipher]>] |
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[B<-in file>] |
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[B<-no_alt_chains>] |
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[B<-certfile file>] |
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[B<-signer file>] |
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[B<-recip file>] |
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[B<-inform SMIME|PEM|DER>] |
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[B<-passin arg>] |
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[B<-inkey file>] |
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[B<-out file>] |
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[B<-outform SMIME|PEM|DER>] |
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[B<-content file>] |
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[B<-to addr>] |
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[B<-from ad>] |
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[B<-subject s>] |
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[B<-text>] |
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[B<-indef>] |
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[B<-noindef>] |
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[B<-stream>] |
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[B<-rand file(s)>] |
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[B<-md digest>] |
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[cert.pem]... |
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=head1 DESCRIPTION |
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The B<smime> command handles S/MIME mail. It can encrypt, decrypt, sign and |
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verify S/MIME messages. |
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=head1 COMMAND OPTIONS |
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There are six operation options that set the type of operation to be performed. |
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The meaning of the other options varies according to the operation type. |
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=over 4 |
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=item B<-encrypt> |
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encrypt mail for the given recipient certificates. Input file is the message |
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to be encrypted. The output file is the encrypted mail in MIME format. |
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Note that no revocation check is done for the recipient cert, so if that |
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key has been compromised, others may be able to decrypt the text. |
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=item B<-decrypt> |
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decrypt mail using the supplied certificate and private key. Expects an |
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encrypted mail message in MIME format for the input file. The decrypted mail |
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is written to the output file. |
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=item B<-sign> |
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sign mail using the supplied certificate and private key. Input file is |
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the message to be signed. The signed message in MIME format is written |
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to the output file. |
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=item B<-verify> |
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verify signed mail. Expects a signed mail message on input and outputs |
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the signed data. Both clear text and opaque signing is supported. |
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=item B<-pk7out> |
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takes an input message and writes out a PEM encoded PKCS#7 structure. |
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=item B<-resign> |
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resign a message: take an existing message and one or more new signers. |
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=item B<-in filename> |
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the input message to be encrypted or signed or the MIME message to |
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be decrypted or verified. |
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=item B<-inform SMIME|PEM|DER> |
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this specifies the input format for the PKCS#7 structure. The default |
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is B<SMIME> which reads an S/MIME format message. B<PEM> and B<DER> |
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format change this to expect PEM and DER format PKCS#7 structures |
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instead. This currently only affects the input format of the PKCS#7 |
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structure, if no PKCS#7 structure is being input (for example with |
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B<-encrypt> or B<-sign>) this option has no effect. |
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=item B<-out filename> |
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the message text that has been decrypted or verified or the output MIME |
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format message that has been signed or verified. |
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=item B<-outform SMIME|PEM|DER> |
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this specifies the output format for the PKCS#7 structure. The default |
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is B<SMIME> which write an S/MIME format message. B<PEM> and B<DER> |
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format change this to write PEM and DER format PKCS#7 structures |
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instead. This currently only affects the output format of the PKCS#7 |
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structure, if no PKCS#7 structure is being output (for example with |
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B<-verify> or B<-decrypt>) this option has no effect. |
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=item B<-stream -indef -noindef> |
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the B<-stream> and B<-indef> options are equivalent and enable streaming I/O |
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for encoding operations. This permits single pass processing of data without |
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the need to hold the entire contents in memory, potentially supporting very |
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large files. Streaming is automatically set for S/MIME signing with detached |
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data if the output format is B<SMIME> it is currently off by default for all |
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other operations. |
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=item B<-noindef> |
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disable streaming I/O where it would produce and indefinite length constructed |
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encoding. This option currently has no effect. In future streaming will be |
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enabled by default on all relevant operations and this option will disable it. |
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=item B<-content filename> |
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This specifies a file containing the detached content, this is only |
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useful with the B<-verify> command. This is only usable if the PKCS#7 |
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structure is using the detached signature form where the content is |
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not included. This option will override any content if the input format |
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is S/MIME and it uses the multipart/signed MIME content type. |
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=item B<-text> |
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this option adds plain text (text/plain) MIME headers to the supplied |
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message if encrypting or signing. If decrypting or verifying it strips |
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off text headers: if the decrypted or verified message is not of MIME |
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type text/plain then an error occurs. |
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=item B<-CAfile file> |
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a file containing trusted CA certificates, only used with B<-verify>. |
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=item B<-CApath dir> |
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a directory containing trusted CA certificates, only used with |
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B<-verify>. This directory must be a standard certificate directory: that |
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is a hash of each subject name (using B<x509 -hash>) should be linked |
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to each certificate. |
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=item B<-md digest> |
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digest algorithm to use when signing or resigning. If not present then the |
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default digest algorithm for the signing key will be used (usually SHA1). |
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=item B<-[cipher]> |
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the encryption algorithm to use. For example DES (56 bits) - B<-des>, |
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triple DES (168 bits) - B<-des3>, |
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EVP_get_cipherbyname() function) can also be used preceded by a dash, for |
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example B<-aes_128_cbc>. See L<B<enc>|enc(1)> for list of ciphers |
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supported by your version of OpenSSL. |
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If not specified triple DES is used. Only used with B<-encrypt>. |
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=item B<-nointern> |
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when verifying a message normally certificates (if any) included in |
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the message are searched for the signing certificate. With this option |
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only the certificates specified in the B<-certfile> option are used. |
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The supplied certificates can still be used as untrusted CAs however. |
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=item B<-noverify> |
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do not verify the signers certificate of a signed message. |
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=item B<-nochain> |
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do not do chain verification of signers certificates: that is don't |
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use the certificates in the signed message as untrusted CAs. |
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=item B<-nosigs> |
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don't try to verify the signatures on the message. |
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=item B<-nocerts> |
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when signing a message the signer's certificate is normally included |
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with this option it is excluded. This will reduce the size of the |
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signed message but the verifier must have a copy of the signers certificate |
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available locally (passed using the B<-certfile> option for example). |
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=item B<-noattr> |
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normally when a message is signed a set of attributes are included which |
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include the signing time and supported symmetric algorithms. With this |
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option they are not included. |
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=item B<-binary> |
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normally the input message is converted to "canonical" format which is |
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effectively using CR and LF as end of line: as required by the S/MIME |
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specification. When this option is present no translation occurs. This |
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is useful when handling binary data which may not be in MIME format. |
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=item B<-nodetach> |
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when signing a message use opaque signing: this form is more resistant |
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to translation by mail relays but it cannot be read by mail agents that |
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do not support S/MIME. Without this option cleartext signing with |
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the MIME type multipart/signed is used. |
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=item B<-certfile file> |
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allows additional certificates to be specified. When signing these will |
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be included with the message. When verifying these will be searched for |
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the signers certificates. The certificates should be in PEM format. |
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=item B<-signer file> |
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a signing certificate when signing or resigning a message, this option can be |
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used multiple times if more than one signer is required. If a message is being |
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verified then the signers certificates will be written to this file if the |
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verification was successful. |
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=item B<-recip file> |
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the recipients certificate when decrypting a message. This certificate |
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must match one of the recipients of the message or an error occurs. |
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=item B<-inkey file> |
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the private key to use when signing or decrypting. This must match the |
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corresponding certificate. If this option is not specified then the |
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private key must be included in the certificate file specified with |
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the B<-recip> or B<-signer> file. When signing this option can be used |
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multiple times to specify successive keys. |
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=item B<-passin arg> |
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the private key password source. For more information about the format of B<arg> |
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see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)|openssl(1)>. |
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=item B<-rand file(s)> |
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a file or files containing random data used to seed the random number |
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generator, or an EGD socket (see L<RAND_egd(3)|RAND_egd(3)>). |
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Multiple files can be specified separated by a OS-dependent character. |
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The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for |
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all others. |
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=item B<cert.pem...> |
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one or more certificates of message recipients: used when encrypting |
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a message. |
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=item B<-to, -from, -subject> |
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the relevant mail headers. These are included outside the signed |
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portion of a message so they may be included manually. If signing |
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then many S/MIME mail clients check the signers certificate's email |
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address matches that specified in the From: address. |
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=item B<-purpose, -ignore_critical, -issuer_checks, -crl_check, -crl_check_all, -policy_check, -extended_crl, -x509_strict, -policy -check_ss_sig -no_alt_chains> |
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Set various options of certificate chain verification. See |
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L<B<verify>|verify(1)> manual page for details. |
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=back |
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=head1 NOTES |
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The MIME message must be sent without any blank lines between the |
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headers and the output. Some mail programs will automatically add |
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a blank line. Piping the mail directly to sendmail is one way to |
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achieve the correct format. |
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The supplied message to be signed or encrypted must include the |
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necessary MIME headers or many S/MIME clients wont display it |
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properly (if at all). You can use the B<-text> option to automatically |
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add plain text headers. |
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A "signed and encrypted" message is one where a signed message is |
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then encrypted. This can be produced by encrypting an already signed |
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message: see the examples section. |
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This version of the program only allows one signer per message but it |
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will verify multiple signers on received messages. Some S/MIME clients |
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choke if a message contains multiple signers. It is possible to sign |
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messages "in parallel" by signing an already signed message. |
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The options B<-encrypt> and B<-decrypt> reflect common usage in S/MIME |
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clients. Strictly speaking these process PKCS#7 enveloped data: PKCS#7 |
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encrypted data is used for other purposes. |
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The B<-resign> option uses an existing message digest when adding a new |
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signer. This means that attributes must be present in at least one existing |
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signer using the same message digest or this operation will fail. |
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The B<-stream> and B<-indef> options enable experimental streaming I/O support. |
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As a result the encoding is BER using indefinite length constructed encoding |
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and no longer DER. Streaming is supported for the B<-encrypt> operation and the |
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B<-sign> operation if the content is not detached. |
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Streaming is always used for the B<-sign> operation with detached data but |
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since the content is no longer part of the PKCS#7 structure the encoding |
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remains DER. |
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=head1 EXIT CODES |
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=over 4 |
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=item Z<>0 |
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the operation was completely successfully. |
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=item Z<>1 |
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an error occurred parsing the command options. |
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=item Z<>2 |
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one of the input files could not be read. |
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=item Z<>3 |
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an error occurred creating the PKCS#7 file or when reading the MIME |
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message. |
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=item Z<>4 |
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an error occurred decrypting or verifying the message. |
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=item Z<>5 |
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the message was verified correctly but an error occurred writing out |
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the signers certificates. |
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=back |
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=head1 EXAMPLES |
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Create a cleartext signed message: |
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openssl smime -sign -in message.txt -text -out mail.msg \ |
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-signer mycert.pem |
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Create an opaque signed message: |
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openssl smime -sign -in message.txt -text -out mail.msg -nodetach \ |
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-signer mycert.pem |
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Create a signed message, include some additional certificates and |
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read the private key from another file: |
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openssl smime -sign -in in.txt -text -out mail.msg \ |
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-signer mycert.pem -inkey mykey.pem -certfile mycerts.pem |
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Create a signed message with two signers: |
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openssl smime -sign -in message.txt -text -out mail.msg \ |
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-signer mycert.pem -signer othercert.pem |
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Send a signed message under Unix directly to sendmail, including headers: |
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openssl smime -sign -in in.txt -text -signer mycert.pem \ |
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-from steve@openssl.org -to someone@somewhere \ |
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-subject "Signed message" | sendmail someone@somewhere |
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Verify a message and extract the signer's certificate if successful: |
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openssl smime -verify -in mail.msg -signer user.pem -out signedtext.txt |
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Send encrypted mail using triple DES: |
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openssl smime -encrypt -in in.txt -from steve@openssl.org \ |
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-to someone@somewhere -subject "Encrypted message" \ |
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-des3 user.pem -out mail.msg |
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Sign and encrypt mail: |
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openssl smime -sign -in ml.txt -signer my.pem -text \ |
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| openssl smime -encrypt -out mail.msg \ |
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-from steve@openssl.org -to someone@somewhere \ |
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-subject "Signed and Encrypted message" -des3 user.pem |
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Note: the encryption command does not include the B<-text> option because the |
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message being encrypted already has MIME headers. |
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Decrypt mail: |
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openssl smime -decrypt -in mail.msg -recip mycert.pem -inkey key.pem |
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The output from Netscape form signing is a PKCS#7 structure with the |
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detached signature format. You can use this program to verify the |
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signature by line wrapping the base64 encoded structure and surrounding |
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it with: |
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-----BEGIN PKCS7----- |
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-----END PKCS7----- |
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and using the command: |
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openssl smime -verify -inform PEM -in signature.pem -content content.txt |
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Alternatively you can base64 decode the signature and use: |
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openssl smime -verify -inform DER -in signature.der -content content.txt |
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Create an encrypted message using 128 bit Camellia: |
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openssl smime -encrypt -in plain.txt -camellia128 -out mail.msg cert.pem |
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Add a signer to an existing message: |
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openssl smime -resign -in mail.msg -signer newsign.pem -out mail2.msg |
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=head1 BUGS |
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The MIME parser isn't very clever: it seems to handle most messages that I've |
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thrown at it but it may choke on others. |
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The code currently will only write out the signer's certificate to a file: if |
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the signer has a separate encryption certificate this must be manually |
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extracted. There should be some heuristic that determines the correct |
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encryption certificate. |
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Ideally a database should be maintained of a certificates for each email |
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address. |
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The code doesn't currently take note of the permitted symmetric encryption |
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algorithms as supplied in the SMIMECapabilities signed attribute. This means the |
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user has to manually include the correct encryption algorithm. It should store |
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the list of permitted ciphers in a database and only use those. |
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No revocation checking is done on the signer's certificate. |
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The current code can only handle S/MIME v2 messages, the more complex S/MIME v3 |
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structures may cause parsing errors. |
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=head1 HISTORY |
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The use of multiple B<-signer> options and the B<-resign> command were first |
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added in OpenSSL 1.0.0 |
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The -no_alt_chains options was first added to OpenSSL 1.0.1n and 1.0.2b. |
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=cut
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