#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);
ffllaaggss is an optional set of flags, which can be used to modify the verify operation.
_P_K_C_S_7___g_e_t_0___s_i_g_n_e_r_s_(_) retrieves the signer's certificates from pp77, it does nnoott check their validity or whether any signatures are valid. The cceerrttss and ffllaaggss parameters have the same meanings as in _P_K_C_S_7___v_e_r_i_f_y_(_).
Initially some sanity checks are performed on pp77. The type of pp77 must be signedData. There must be at least one signature on the data and if the content is detached iinnddaattaa cannot be NNUULLLL.
An attempt is made to locate all the signer's certificates, first looking in the cceerrttss parameter (if it is not NNUULLLL) and then looking in any certificates contained in the pp77 structure itself. If any signer's certificates cannot be located the operation fails.
Each signer's certificate is chain verified using the ssmmiimmeessiiggnn 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 oouutt is 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 (ored together) can be passed in the ffllaaggss parameter to change the default verify behaviour. Only the flag PPKKCCSS77__NNOOIINNTTEERRNN is meaningful to _P_K_C_S_7___g_e_t_0___s_i_g_n_e_r_s_(_).
If PPKKCCSS77__NNOOIINNTTEERRNN is set the certificates in the message itself are not searched when locating the signer's certificate. This means that all the signers certificates must be in the cceerrttss parameter.
If the PPKKCCSS77__TTEEXXTT flag is set MIME headers for type tteexxtt//ppllaaiinn are deleted from the content. If the content is not of type tteexxtt//ppllaaiinn then an error is returned.
If PPKKCCSS77__NNOOVVEERRIIFFYY is set the signer's certificates are not chain verified.
If PPKKCCSS77__NNOOCCHHAAIINN 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 PPKKCCSS77__NNOOSSIIGGSS is set then the signatures on the data are not checked.
Care should be taken when modifying the default verify behaviour, for example setting PPKKCCSS77__NNOOVVEERRIIFFYY||PPKKCCSS77__NNOOSSIIGGSS 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 oouutt 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).
_P_K_C_S_7___g_e_t_0___s_i_g_n_e_r_s_(_) returns all signers or NNUULLLL if an error occurred.
The error can be obtained from _E_R_R___g_e_t___e_r_r_o_r(3)
The lack of single pass processing and need to hold all data in memory as mentioned in _P_K_C_S_7___s_i_g_n_(_) also applies to _P_K_C_S_7___v_e_r_i_f_y_(_).