On Thu, Feb 10, 2000 at 02:44:31PM -0500, Adam Sherman wrote: > On Thu, Feb 10, 2000 at 06:57:32AM -0800, Claus Assmann wrote: > > On Thu, Feb 10, 2000, Thomas Roessler wrote: > > > On 2000-02-09 18:15:03 -0500, Adam Sherman wrote: > > > > > > > Would it be possible to use Mutt with S/MIME cryptography? > > > > > > It wouldn't be difficult to add support for this to mutt, once you > > > have a command-line based tool with the cryptographic functionality. > > > > openssl has this for some time now, but it's just in the snapshots, > > not yet released. I tried to verify some signatures and it works > > fine. > > This sounds good, I will try to build a list of commands and I'll send > to the list. I found the attached document in the docs/apps directory of the latest OpenSSL SNAPSHOT. It describes the command syntaxe of the smime openssl command. Also attached is the appropriate rfc (2632). I'm not a C programmer, and I don't know where to start with regards to implementing this. Any pointers? Thanks, A. -- Adam Sherman <[EMAIL PROTECTED]> +1 (613) 223-5746
Network Working Group B. Ramsdell, Editor Request for Comments: 2632 Worldtalk Category: Standards Track June 1999 S/MIME Version 3 Certificate Handling Status of this Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (1999). All Rights Reserved. 1. Overview S/MIME (Secure/Multipurpose Internet Mail Extensions), described in [SMIME-MSG], provides a method to send and receive secure MIME messages. Before using a public key to provide security services, the S/MIME agent MUST certify that the public key is valid. S/MIME agents MUST use PKIX certificates to validate public keys as described in the Internet X.509 Public Key Infrastructure (PKIX) Certificate and CRL Profile [KEYM]. S/MIME agents MUST meet the certificate processing requirements documented in this document in addition to those stated in [KEYM]. This specification is compatible with the Cryptographic Message Syntax [CMS] in that it uses the data types defined by CMS. It also inherits all the varieties of architectures for certificate-based key management supported by CMS. 1.1 Definitions For the purposes of this memo, the following definitions apply. ASN.1: Abstract Syntax Notation One, as defined in ITU-T X.680-689. Attribute Certificate (AC): An X.509 AC is a separate structure from a subject's public key X.509 Certificate. A subject may have multiple X.509 ACs associated with each of its public key X.509 Certificates. Each X.509 AC binds one or more Attributes with one of the subject's public key X.509 Certificates. The X.509 AC syntax is defined in [X.509] Ramsdell Standards Track [Page 1] RFC 2632 S/MIME Version 3 Certificate Handling June 1999 BER: Basic Encoding Rules for ASN.1, as defined in ITU-T X.690. Certificate: A type that binds an entity's distinguished name to a public key with a digital signature. This type is defined in the Internet X.509 Public Key Infrastructure (PKIX) Certificate and CRL Profile [KEYM]. This type also contains the distinguished name of the certificate issuer (the signer), an issuer-specific serial number, the issuer's signature algorithm identifier, a validity period, and extensions also defined in that document. Certificate Revocation List (CRL): A type that contains information about certificates whose validity an issuer has prematurely revoked. The information consists of an issuer name, the time of issue, the next scheduled time of issue, a list of certificate serial numbers and their associated revocation times, and extensions as defined in [KEYM]. The CRL is signed by the issuer. The type intended by this specification is the one defined in [KEYM]. DER: Distinguished Encoding Rules for ASN.1, as defined in ITU-T X.690. Receiving agent: software that interprets and processes S/MIME CMS objects, MIME body parts that contain CMS objects, or both. Sending agent: software that creates S/MIME CMS objects, MIME body parts that contain CMS objects, or both. S/MIME agent: user software that is a receiving agent, a sending agent, or both. 1.2 Compatibility with Prior Practice of S/MIME S/MIME version 3 agents should attempt to have the greatest interoperability possible with S/MIME version 2 agents. S/MIME version 2 is described in RFC 2311 through RFC 2315, inclusive. RFC 2311 also has historical information about the development of S/MIME. 1.3 Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [MUSTSHOULD]. Ramsdell Standards Track [Page 2] RFC 2632 S/MIME Version 3 Certificate Handling June 1999 2. CMS Options The CMS message format allows for a wide variety of options in content and algorithm support. This section puts forth a number of support requirements and recommendations in order to achieve a base level of interoperability among all S/MIME implementations. Most of the CMS format for S/MIME messages is defined in [SMIME-MSG]. 2.1 CertificateRevocationLists Receiving agents MUST support the Certificate Revocation List (CRL) format defined in [KEYM]. If sending agents include CRLs in outgoing messages, the CRL format defined in [KEYM] MUST be used. All agents MUST be capable of performing revocation checks using CRLs as specified in [KEYM]. All agents MUST perform revocation status checking in accordance with [KEYM]. Receiving agents MUST recognize CRLs in received S/MIME messages. Agents SHOULD store CRLs received in messages for use in processing later messages. Agents MUST handle multiple valid Certificate Authority (CA) certificates containing the same subject name and the same public keys but with overlapping validity intervals. 2.2 CertificateChoices Receiving agents MUST support PKIX v1 and PKIX v3 certificates. See [KEYM] for details about the profile for certificate formats. End entity certificates MAY include an Internet mail address, as described in section 3.1. Receiving agents SHOULD support X.509 attribute certificates. 2.2.1 Historical Note About CMS Certificates The CMS message format supports a choice of certificate formats for public key content types: PKIX, PKCS #6 Extended Certificates and X.509 Attribute Certificates. The PKCS #6 format is not in widespread use. In addition, PKIX certificate extensions address much of the same functionality and flexibility as was intended in the PKCS #6. Thus, sending and receiving agents MUST NOT use PKCS #6 extended certificates. Ramsdell Standards Track [Page 3] RFC 2632 S/MIME Version 3 Certificate Handling June 1999 2.3 CertificateSet Receiving agents MUST be able to handle an arbitrary number of certificates of arbitrary relationship to the message sender and to each other in arbitrary order. In many cases, the certificates included in a signed message may represent a chain of certification from the sender to a particular root. There may be, however, situations where the certificates in a signed message may be unrelated and included for convenience. Sending agents SHOULD include any certificates for the user's public key(s) and associated issuer certificates. This increases the likelihood that the intended recipient can establish trust in the originator's public key(s). This is especially important when sending a message to recipients that may not have access to the sender's public key through any other means or when sending a signed message to a new recipient. The inclusion of certificates in outgoing messages can be omitted if S/MIME objects are sent within a group of correspondents that has established access to each other's certificates by some other means such as a shared directory or manual certificate distribution. Receiving S/MIME agents SHOULD be able to handle messages without certificates using a database or directory lookup scheme. A sending agent SHOULD include at least one chain of certificates up to, but not including, a Certificate Authority (CA) that it believes that the recipient may trust as authoritative. A receiving agent SHOULD be able to handle an arbitrarily large number of certificates and chains. Agents MAY send CA certificates, that is, certificates that are self-signed and can be considered the "root" of other chains. Note that receiving agents SHOULD NOT simply trust any self-signed certificates as valid CAs, but SHOULD use some other mechanism to determine if this is a CA that should be trusted. Also note that in the case of DSA certificates the parameters may be located in the root certificate. This would require that the recipient possess the root certificate in order to perform a signature verification, and is a valid example of a case where transmitting the root certificate may be required. Receiving agents MUST support chaining based on the distinguished name fields. Other methods of building certificate chains may be supported but are not currently recommended. Ramsdell Standards Track [Page 4] RFC 2632 S/MIME Version 3 Certificate Handling June 1999 Receiving agents SHOULD support the decoding of X.509 attribute certificates included in CMS objects. All other issues regarding the generation and use of X.509 attribute certificates are outside of the scope of this specification. 3. Using Distinguished Names for Internet Mail End-entity certificates MAY contain an Internet mail address as described in [RFC-822]. The address must be an "addr-spec" as defined in Section 6.1 of that specification. The email address SHOULD be in the subjectAltName extension, and SHOULD NOT be in the subject distinguished name. Receiving agents MUST recognize email addresses in the subjectAltName field. Receiving agents MUST recognize email addresses in the Distinguished Name field in the PKCS #9 emailAddress attribute. Sending agents SHOULD make the address in the From or Sender header in a mail message match an Internet mail address in the signer's certificate. Receiving agents MUST check that the address in the From or Sender header of a mail message matches an Internet mail address in the signer's certificate, if mail addresses are present in the certificate. A receiving agent SHOULD provide some explicit alternate processing of the message if this comparison fails, which may be to display a message that shows the recipient the addresses in the certificate or other certificate details. All subject and issuer names MUST be populated (i.e. not an empty SEQUENCE) in S/MIME-compliant PKIX certificates, except that the subject DN in a user's (i.e. end-entity) certificate MAY be an empty SEQUENCE in which case the subjectAltName extension will include the subject's identifier and MUST be marked as critical. 4. Certificate Processing A receiving agent needs to provide some certificate retrieval mechanism in order to gain access to certificates for recipients of digital envelopes. There are many ways to implement certificate retrieval mechanisms. X.500 directory service is an excellent example of a certificate retrieval-only mechanism that is compatible with classic X.500 Distinguished Names. The PKIX Working Group is investigating other mechanisms such as directory servers. Another method under consideration by the IETF is to provide certificate retrieval services as part of the existing Domain Name System (DNS). Until such mechanisms are widely used, their utility may be limited by the small number of correspondent's certificates that can be Ramsdell Standards Track [Page 5] RFC 2632 S/MIME Version 3 Certificate Handling June 1999 retrieved. At a minimum, for initial S/MIME deployment, a user agent could automatically generate a message to an intended recipient requesting that recipient's certificate in a signed return message. Receiving and sending agents SHOULD also provide a mechanism to allow a user to "store and protect" certificates for correspondents in such a way so as to guarantee their later retrieval. In many environments, it may be desirable to link the certificate retrieval/storage mechanisms together in some sort of certificate database. In its simplest form, a certificate database would be local to a particular user and would function in a similar way as a "address book" that stores a user's frequent correspondents. In this way, the certificate retrieval mechanism would be limited to the certificates that a user has stored (presumably from incoming messages). A comprehensive certificate retrieval/storage solution may combine two or more mechanisms to allow the greatest flexibility and utility to the user. For instance, a secure Internet mail agent may resort to checking a centralized certificate retrieval mechanism for a certificate if it can not be found in a user's local certificate storage/retrieval database. Receiving and sending agents SHOULD provide a mechanism for the import and export of certificates, using a CMS certs-only message. This allows for import and export of full certificate chains as opposed to just a single certificate. This is described in [SMIME- MSG]. 4.1 Certificate Revocation Lists In general, it is always better to get the latest CRL information from a CA than to get information stored away from incoming messages. A receiving agent SHOULD have access to some certificate-revocation list (CRL) retrieval mechanism in order to gain access to certificate-revocation information when validating certificate chains. A receiving or sending agent SHOULD also provide a mechanism to allow a user to store incoming certificate-revocation information for correspondents in such a way so as to guarantee its later retrieval. Receiving and sending agents SHOULD retrieve and utilize CRL information every time a certificate is verified as part of a certificate chain validation even if the certificate was already verified in the past. However, in many instances (such as off-line verification) access to the latest CRL information may be difficult or impossible. The use of CRL information, therefore, may be dictated by the value of the information that is protected. The value of the Ramsdell Standards Track [Page 6] RFC 2632 S/MIME Version 3 Certificate Handling June 1999 CRL information in a particular context is beyond the scope of this memo but may be governed by the policies associated with particular certificate hierarchies. All agents MUST be capable of performing revocation checks using CRLs as specified in [KEYM]. All agents MUST perform revocation status checking in accordance with [KEYM]. Receiving agents MUST recognize CRLs in received S/MIME messages. 4.2 Certificate Chain Validation In creating a user agent for secure messaging, certificate, CRL, and certificate chain validation SHOULD be highly automated while still acting in the best interests of the user. Certificate, CRL, and chain validation MUST be performed as per [KEYM] when validating a correspondent's public key. This is necessary before using a public key to provide security services such as: verifying a signature; encrypting a content-encryption key (ex: RSA); or forming a pairwise symmetric key (ex: Diffie-Hellman) to be used to encrypt or decrypt a content-encryption key. Certificates and CRLs are made available to the chain validation procedure in two ways: a) incoming messages, and b) certificate and CRL retrieval mechanisms. Certificates and CRLs in incoming messages are not required to be in any particular order nor are they required to be in any way related to the sender or recipient of the message (although in most cases they will be related to the sender). Incoming certificates and CRLs SHOULD be cached for use in chain validation and optionally stored for later use. This temporary certificate and CRL cache SHOULD be used to augment any other certificate and CRL retrieval mechanisms for chain validation on incoming signed messages. 4.3 Certificate and CRL Signing Algorithms Certificates and Certificate-Revocation Lists (CRLs) are signed by the certificate issuer. A receiving agent MUST be capable of verifying the signatures on certificates and CRLs made with id-dsa- with-sha1 [DSS]. A receiving agent SHOULD be capable of verifying the signatures on certificates and CRLs made with md2WithRSAEncryption, md5WithRSAEncryption and sha-1WithRSAEncryption signature algorithms with key sizes from 512 bits to 2048 bits described in [PKCS#1V2]. Ramsdell Standards Track [Page 7] RFC 2632 S/MIME Version 3 Certificate Handling June 1999 4.4 PKIX Certificate Extensions PKIX describes an extensible framework in which the basic certificate information can be extended and how such extensions can be used to control the process of issuing and validating certificates. The PKIX Working Group has ongoing efforts to identify and create extensions which have value in particular certification environments. Further, there are active efforts underway to issue PKIX certificates for business purposes. This document identifies the minumum required set of certificate extensions which have the greatest value in the S/MIME environment. The syntax and semantics of all the identified extensions are defined in [KEYM]. Sending and receiving agents MUST correctly handle the Basic Constraints Certificate Extension, the Key Usage Certificate Extension, authorityKeyID, subjectKeyID, and the subjectAltNames when they appear in end-user certificates. Some mechanism SHOULD exist to handle the defined certificate extensions when they appear in intermediate or CA certificates. Certificates issued for the S/MIME environment SHOULD NOT contain any critical extensions (extensions that have the critical field set to TRUE) other than those listed here. These extensions SHOULD be marked as non-critical unless the proper handling of the extension is deemed critical to the correct interpretation of the associated certificate. Other extensions may be included, but those extensions SHOULD NOT be marked as critical. Interpretation and syntax for all extensions MUST follow [KEYM], unless otherwise specified here. 4.4.1 Basic Constraints Certificate Extension The basic constraints extension serves to delimit the role and position of an issuing authority or end-entity certificate plays in a chain of certificates. For example, certificates issued to CAs and subordinate CAs contain a basic constraint extension that identifies them as issuing authority certificates. End-entity certificates contain an extension that constrains the certificate from being an issuing authority certificate. Certificates SHOULD contain a basicConstraints extension in CA certificates, and SHOULD NOT contain that extension in end entity certificates. Ramsdell Standards Track [Page 8] RFC 2632 S/MIME Version 3 Certificate Handling June 1999 4.4.2 Key Usage Certificate Extension The key usage extension serves to limit the technical purposes for which a public key listed in a valid certificate may be used. Issuing authority certificates may contain a key usage extension that restricts the key to signing certificates, certificate revocation lists and other data. For example, a certification authority may create subordinate issuer certificates which contain a keyUsage extension which specifies that the corresponding public key can be used to sign end user certs and sign CRLs. If a key usage extension is included in a PKIX certificate, then it MUST be marked as critical. 4.4.2.1 Key Usage in Diffie-Hellman Key Exchange Certificates For Diffie-Hellman key exchange certificates (certificates in which the subject public key algorithm is dhpublicnumber), if the keyUsage keyAgreement bit is set to 1 AND if the public key is to be used to form a pairwise key to decrypt data, then the S/MIME agent MUST only use the public key if the keyUsage encipherOnly bit is set to 0. If the keyUsage keyAgreement bit is set to 1 AND if the key is to be used to form a pairwise key to encrypt data, then the S/MIME agent MUST only use the public key if the keyUsage decipherOnly bit is set to 0. 4.4.3 Subject Alternative Name Extension The subject alternative name extension is used in S/MIME as the preferred means to convey the RFC-822 email address(es) that correspond to the entity for this certificate. Any RFC-822 email addresses present MUST be encoded using the rfc822Name CHOICE of the GeneralName type. Since the SubjectAltName type is a SEQUENCE OF GeneralName, multiple RFC-822 email addresses MAY be present. 5. Security Considerations All of the security issues faced by any cryptographic application must be faced by a S/MIME agent. Among these issues are protecting the user's private key, preventing various attacks, and helping the user avoid mistakes such as inadvertently encrypting a message for the wrong recipient. The entire list of security considerations is beyond the scope of this document, but some significant concerns are listed here. Ramsdell Standards Track [Page 9] RFC 2632 S/MIME Version 3 Certificate Handling June 1999 When processing certificates, there are many situations where the processing might fail. Because the processing may be done by a user agent, a security gateway, or other program, there is no single way to handle such failures. Just because the methods to handle the failures has not been listed, however, the reader should not assume that they are not important. The opposite is true: if a certificate is not provably valid and associated with the message, the processing software should take immediate and noticable steps to inform the end user about it. Some of the many places where signature and certificate checking might fail include: - no Internet mail addresses in a certificate match the sender of a message - no certificate chain leads to a trusted CA - no ability to check the CRL for a certificate - an invalid CRL was received - the CRL being checked is expired - the certificate is expired - the certificate has been revoked There are certainly other instances where a certificate may be invalid, and it is the responsibility of the processing software to check them all thoroughly, and to decide what to do if the check fails. Ramsdell Standards Track [Page 10] RFC 2632 S/MIME Version 3 Certificate Handling June 1999 A. References [CERTV2] Dusse, S., Hoffman, P. and B. Ramsdell,"S/MIME Version 2 Certificate Handling", RFC 2312, March 1998. [CMS] Housley, R., "Cryptographic Message Syntax", RFC 2630, June 1999. [DSS] NIST FIPS PUB 186, "Digital Signature Standard", 18 May 1994. [KEYM] Housley, R., Ford, W., Polk, W. and D. Solo, "Internet X.509 Public Key Infrastructure Certificate and CRL Profile", RFC 2459, January 1999. [MUSTSHOULD] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [PKCS#1V2] Kaliski, B., "PKCS #1: RSA Cryptography Specifications Version 2.0", RFC 2437, October 1998. [RFC-822] Crocker, D., "Standard For The Format Of ARPA Internet Text Messages", STD 11, RFC 822, August 1982. [SMIME-MSG] Ramsdell, B., Editor, "S/MIME Version 3 Message Specification", RFC 2633, June 1999. [X.500] ITU-T Recommendation X.500 (1997) | ISO/IEC 9594-1:1997, Information technology - Open Systems Interconnection - The Directory: Overview of concepts, models and services. [X.501] ITU-T Recommendation X.501 (1997) | ISO/IEC 9594-2:1997, Information technology - Open Systems Interconnection - The Directory: Models. [X.509] ITU-T Recommendation X.509 (1997) | ISO/IEC 9594-8:1997, Information technology - Open Systems Interconnection - The Directory: Authentication framework. [X.520] ITU-T Recommendation X.520 (1997) | ISO/IEC 9594-6:1997, Information technology - Open Systems Interconnection - The Directory: Selected attribute types. Ramsdell Standards Track [Page 11] RFC 2632 S/MIME Version 3 Certificate Handling June 1999 B. Acknowledgements Many thanks go out to the other authors of the S/MIME v2 RFC: Steve Dusse, Paul Hoffman and Jeff Weinstein. Without v2, there wouldn't be a v3. A number of the members of the S/MIME Working Group have also worked very hard and contributed to this document. Any list of people is doomed to omission and for that I apologize. In alphabetical order, the following people stand out in my mind due to the fact that they made direct contributions to this document. Bill Flanigan Elliott Ginsburg Paul Hoffman Russ Housley Michael Myers John Pawling Denis Pinkas Jim Schaad Editor's Address Blake Ramsdell Worldtalk 17720 NE 65th St Ste 201 Redmond, WA 98052 Phone: +1 425 376 0225 EMail: [EMAIL PROTECTED] Ramsdell Standards Track [Page 12] RFC 2632 S/MIME Version 3 Certificate Handling June 1999 Full Copyright Statement Copyright (C) The Internet Society (1999). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. Ramsdell Standards Track [Page 13]
NAME smime - S/MIME utility SYNOPSIS openssl smime [-encrypt] [-decrypt] [-sign] [-verify] [-pk7out] [-des] [-des3] [-rc2-40] [-rc2-64] [-rc2-128] [-in file] [- certfile file] [-signer file] [-recip file] [-in file] [-inkey file] [-out file] [-to addr] [-from ad] [-subject s] [-text] [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. -out filename the message text that has been decrypted or verified or the output MIME format message that has been signed or verified. -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 the encryption algorithm to use. DES (56 bits), triple DES (168 bits) or 40, 64 or 128 bit RC2 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. 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 [EMAIL PROTECTED] -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 [EMAIL PROTECTED] \ -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 -encrypt -out mail.msg \ -from [EMAIL PROTECTED] -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 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.