250 lines
8.7 KiB
Groff
250 lines
8.7 KiB
Groff
.\" $NetBSD: PKCS7_verify.3,v 1.2 2004/03/20 21:48:46 groo Exp $
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.\" ======================================================================
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.\"
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.IX Title "PKCS7_verify 3"
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.TH PKCS7_verify 3 "0.9.7d" "2003-07-24" "OpenSSL"
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.UC
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.SH "NAME"
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PKCS7_verify \- verify a PKCS#7 signedData structure
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.SH "LIBRARY"
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libcrypto, -lcrypto
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.SH "SYNOPSIS"
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.IX Header "SYNOPSIS"
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int PKCS7_verify(\s-1PKCS7\s0 *p7, STACK_OF(X509) *certs, X509_STORE *store, \s-1BIO\s0 *indata, \s-1BIO\s0 *out, int flags);
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.PP
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int PKCS7_get0_signers(\s-1PKCS7\s0 *p7, STACK_OF(X509) *certs, int flags);
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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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\&\fIPKCS7_verify()\fR verifies a PKCS#7 signedData structure. \fBp7\fR is the \s-1PKCS7\s0
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structure to verify. \fBcerts\fR is a set of certificates in which to search for
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the signer's certificate. \fBstore\fR is a trusted certficate store (used for
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chain verification). \fBindata\fR is the signed data if the content is not
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present in \fBp7\fR (that is it is detached). The content is written to \fBout\fR
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if it is not \s-1NULL\s0.
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.PP
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\&\fBflags\fR is an optional set of flags, which can be used to modify the verify
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operation.
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.PP
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\&\fIPKCS7_get0_signers()\fR retrieves the signer's certificates from \fBp7\fR, it does
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\&\fBnot\fR check their validity or whether any signatures are valid. The \fBcerts\fR
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and \fBflags\fR parameters have the same meanings as in \fIPKCS7_verify()\fR.
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.SH "VERIFY PROCESS"
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.IX Header "VERIFY PROCESS"
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Normally the verify process proceeds as follows.
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.PP
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Initially some sanity checks are performed on \fBp7\fR. The type of \fBp7\fR must
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be signedData. There must be at least one signature on the data and if
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the content is detached \fBindata\fR cannot be \fB\s-1NULL\s0\fR.
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.PP
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An attempt is made to locate all the signer's certificates, first looking in
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the \fBcerts\fR parameter (if it is not \fB\s-1NULL\s0\fR) and then looking in any certificates
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contained in the \fBp7\fR structure itself. If any signer's certificates cannot be
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located the operation fails.
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.PP
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Each signer's certificate is chain verified using the \fBsmimesign\fR purpose and
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the supplied trusted certificate store. Any internal certificates in the message
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are used as untrusted CAs. If any chain verify fails an error code is returned.
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.PP
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Finally the signed content is read (and written to \fBout\fR is it is not \s-1NULL\s0) and
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the signature's checked.
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.PP
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If all signature's verify correctly then the function is successful.
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.PP
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Any of the following flags (ored together) can be passed in the \fBflags\fR parameter
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to change the default verify behaviour. Only the flag \fB\s-1PKCS7_NOINTERN\s0\fR is
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meaningful to \fIPKCS7_get0_signers()\fR.
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.PP
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If \fB\s-1PKCS7_NOINTERN\s0\fR is set the certificates in the message itself are not
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searched when locating the signer's certificate. This means that all the signers
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certificates must be in the \fBcerts\fR parameter.
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.PP
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If the \fB\s-1PKCS7_TEXT\s0\fR flag is set \s-1MIME\s0 headers for type \fBtext/plain\fR are deleted
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from the content. If the content is not of type \fBtext/plain\fR then an error is
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returned.
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.PP
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If \fB\s-1PKCS7_NOVERIFY\s0\fR is set the signer's certificates are not chain verified.
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.PP
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If \fB\s-1PKCS7_NOCHAIN\s0\fR is set then the certificates contained in the message are
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not used as untrusted CAs. This means that the whole verify chain (apart from
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the signer's certificate) must be contained in the trusted store.
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.PP
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If \fB\s-1PKCS7_NOSIGS\s0\fR is set then the signatures on the data are not checked.
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.SH "NOTES"
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.IX Header "NOTES"
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One application of \fB\s-1PKCS7_NOINTERN\s0\fR is to only accept messages signed by
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a small number of certificates. The acceptable certificates would be passed
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in the \fBcerts\fR parameter. In this case if the signer is not one of the
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certificates supplied in \fBcerts\fR then the verify will fail because the
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signer cannot be found.
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.PP
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Care should be taken when modifying the default verify behaviour, for example
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setting \fBPKCS7_NOVERIFY|PKCS7_NOSIGS\fR will totally disable all verification
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and any signed message will be considered valid. This combination is however
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useful if one merely wishes to write the content to \fBout\fR and its validity
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is not considered important.
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.PP
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Chain verification should arguably be performed using the signing time rather
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than the current time. However since the signing time is supplied by the
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signer it cannot be trusted without additional evidence (such as a trusted
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timestamp).
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.SH "RETURN VALUES"
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.IX Header "RETURN VALUES"
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\&\fIPKCS7_verify()\fR returns 1 for a successful verification and zero or a negative
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value if an error occurs.
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.PP
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\&\fIPKCS7_get0_signers()\fR returns all signers or \fB\s-1NULL\s0\fR if an error occurred.
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.PP
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The error can be obtained from ERR_get_error(3)
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.SH "BUGS"
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.IX Header "BUGS"
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The trusted certificate store is not searched for the signers certificate,
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this is primarily due to the inadequacies of the current \fBX509_STORE\fR
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functionality.
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.PP
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The lack of single pass processing and need to hold all data in memory as
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mentioned in \fIPKCS7_sign()\fR also applies to \fIPKCS7_verify()\fR.
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.SH "SEE ALSO"
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.IX Header "SEE ALSO"
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ERR_get_error(3), PKCS7_sign(3)
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.SH "HISTORY"
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.IX Header "HISTORY"
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\&\fIPKCS7_verify()\fR was added to OpenSSL 0.9.5
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