--- name: "libressl-PKCS7_verify" section: "3" platform: "linux" package: "libressl" version: "4.4.0-1" release: "Arch Linux 2026-11-01" platforms: ["linux"] url: "https://new.carta.tech/libressl-PKCS7_verify" --- # libressl-PKCS7\_verify(3) verify a PKCS#7 signedData structure ## NAME **PKCS7\_verify**, **PKCS7\_get0\_signers** – verify a PKCS#7 signedData structure ## SYNOPSIS Crypto Library (libcrypto, -lcrypto) **#include \** *int*\ **PKCS7\_verify**(*PKCS7 \*p7*, *STACK\_OF(X509) \*certs*, *X509\_STORE \*store*, *BIO \*indata*, *BIO \*out*, *int flags*); *STACK\_OF(X509)* *\**\ **PKCS7\_get0\_signers**(*PKCS7 \*p7*, *STACK\_OF(X509) \*certs*, *int flags*); ## DESCRIPTION **PKCS7\_verify**() verifies a PKCS#7 signedData structure. *p7* is the *PKCS7* structure to verify. *certs* is a set of certificates in which to search for the signer's certificate. *store* is a trusted certificate store (used for chain verification). *indata* is the signed data if the content is not present in *p7*, that is if it is detached. The content is written to *out* if it is not NULL. *flags* is an optional set of flags, which can be used to modify the verify operation. **PKCS7\_get0\_signers**() retrieves the signer's certificates from *p7*. The signers must be freed with **sk\_X509\_free**(). It does **not** check their validity or whether any signatures are valid. The *certs* and *flags* parameters have the same meanings as in **PKCS7\_verify**(). Normally the verify process proceeds as follows. Initially some sanity checks are performed on *p7*. The type of *p7* must be signedData. There must be at least one signature on the data and if the content is detached, *indata* cannot be NULL. If the content is not detached and *indata* is not *NULL*, then the structure has both embedded and external content. To treat this as an error, use the flag PKCS7\_NO\_DUAL\_CONTENT. The default behavior allows this, for compatibility with other implementations. An attempt is made to locate all the signer's certificates, first looking in the *certs* parameter (if it is not NULL) and then looking in any certificates contained in the *p7* structure itself. If any signer's certificates cannot be located, the operation fails. Each signer's certificate is chain verified using the **smimesign** purpose and the supplied trusted certificate store. Any internal certificates in the message are used as untrusted CAs. If any chain verify fails, an error code is returned. Finally, the signed content is read (and written to *out* if it is not NULL) and the signature's checked. If all signature's verify correctly then the function is successful. Any of the following flags (OR'ed together) can be passed in the *flags* parameter to change the default verify behaviour. Only the flag PKCS7\_NOINTERN is meaningful to **PKCS7\_get0\_signers**(). If PKCS7\_NOINTERN is set, the certificates in the message itself are not searched when locating the signer's certificate. This means that all the signer's certificates must be in the *certs* parameter. If the PKCS7\_TEXT flag is set, MIME headers for type **text/plain** are deleted from the content. If the content is not of type **text/plain**, then an error is returned. If PKCS7\_NOVERIFY is set, the signer's certificates are not chain verified. If PKCS7\_NOCHAIN is set, then the certificates contained in the message are not used as untrusted CAs. This means that the whole verify chain (apart from the signer's certificate) must be contained in the trusted store. If PKCS7\_NOSIGS is set, then the signatures on the data are not checked. One application of PKCS7\_NOINTERN is to only accept messages signed by a small number of certificates. The acceptable certificates would be passed in the *certs* parameter. In this case, if the signer is not one of the certificates supplied in *certs*, then the verify will fail because the signer cannot be found. Care should be taken when modifying the default verify behaviour, for example setting PKCS7\_NOVERIFY \| PKCS7\_NOSIGS will totally disable all verification and any signed message will be considered valid. This combination is however useful if one merely wishes to write the content to *out* and its validity is not considered important. Chain verification should arguably be performed using the signing time rather than the current time. However since the signing time is supplied by the signer, it cannot be trusted without additional evidence (such as a trusted timestamp). ## RETURN VALUES **PKCS7\_verify**() returns 1 for a successful verification and 0 or a negative value if an error occurs. **PKCS7\_get0\_signers**() returns all signers or NULL if an error occurred. The signers must be freed with **sk\_X509\_free**(). The error can be obtained from ERR\_get\_error(3). ## SEE ALSO PKCS7\_decrypt(3), PKCS7\_new(3), PKCS7\_sign(3), X509\_STORE\_new(3) ## HISTORY **PKCS7\_verify**() and **PKCS7\_get0\_signers**() first appeared in OpenSSL 0.9.5 and have been available since OpenBSD 2.7. ## BUGS The trusted certificate store is not searched for the signer's certificate. This is primarily due to the inadequacies of the current *X509\_STORE* functionality. The lack of single pass processing and the need to hold all data in memory as mentioned in PKCS7\_sign(3) also applies to **PKCS7\_verify**().