Dear All, Thank you Dave Thompson for your help and clarifying my doubt.
Thank you. Regards, --Ajeet Kumar Singh Sarve Bhavantu Sukhina ,Sarve Santu NiramayaSarve Bhadrani Pashyantu , Maa Kaschit Dukha Bhagh Bhavet -----Original Message----- From: owner-openssl-us...@openssl.org [mailto:owner-openssl-us...@openssl.org] On Behalf Of Dave Thompson Sent: Saturday, January 31, 2009 8:11 AM To: openssl-users@openssl.org Subject: RE: Openssl signature verification > From: owner-openssl-us...@openssl.org On Behalf Of Ajeet kumar.S > Sent: Friday, 30 January, 2009 00:07 > In openssl API X509_verify(X509 *a, EVP_PKEY *r) is used to verify > the signature of certificate. I have some doubt please help me. > Is in this API we are passing the CA certificate and public key of CA certificate? We pass any cert and the key we believe (are told) will verify it. CA "root" certs are self-signed; the key _in_ the cert is used to sign it, or to be precise the keypair whose public half is in the cert is used. As a result you can't trust a root cert simply because the signature verifies; you must have other evidence this is the/a valid root cert from/for a given CA, such as a trusted distribution or manually-checked fingerprint. Lower-level CA certs (if any) and end-entity certs are signed "by" a parent cert, or to be precise by a keypair whose public half is certified by the parent cert. If you instead use X509_verify_cert, it tries several methods to find and verify the whole cert chain (from a root) by looking in (data from) a configurable file and/or (hashed) entries in a configurable directory. If you want to do this job or part(s) of it yourself, you can look at that for an example, but it's pretty complicated. > What is data over SSL compute the HASH? The DER-encoded CertificateInfo portion of the cert, which is the first element in the outermost SEQUENCE and contains version, serial, copy of sig-algid, issuer name, subject name & publickey, validity period, and for v3 optional extensions such as keyusage, subjectaltname, keyids, etc. This is everything "in" the cert except the appended algid and signature, and is indented under "Data:" in the display from openssl x509 -text . > SSL will decrypt the CA signature (Which is on CA certificate bundle)? > Decrypted CA Signature will match to above HASH.(query 2)? For RSA signatures this is approximately true. You actually raise the signature value to the public exponent (like RSA encryption) rather than the private exponent (as for RSA decryption), and the (standard) padding is different for sign/verify than for encrypt/decrypt. For DSA signatures this is not true at all. There is no corresponding encryption or decryption; there is simply a signing algorithm and a verifying algorithm. You apply the verifying algorithm to determine if the received signature is correct for the (recomputed) hash. You separately asked > In Openssl for signature verification we are using API ASN1_item_verify(). > Let me know the data which is used for finger print (signature) creation > is the CA public key or some thing else data . > Please clarify this doubt. How we are verifying the signature? If you mean in crypto/x509/x_all.c X509_verify(), we are verifying the signature in the cert, of the data in the cert, using the key. No fingerprint is involved. This only applies to X509 certs; the verification of signatures on other things is similar but not identical. Fingerprints can be used in lots of situations and ways. _PKI_ fingerprints can meaningfully be computed on either the whole CertificateInfo thus verifying all the attributes directly, or just on the publickey since that is enough to verify the signature. But a fingerprint is not a signature; it does not itself have any cryptographic protection. ______________________________________________________________________ OpenSSL Project http://www.openssl.org User Support Mailing List openssl-users@openssl.org Automated List Manager majord...@openssl.org ______________________________________________________________________ OpenSSL Project http://www.openssl.org User Support Mailing List openssl-users@openssl.org Automated List Manager majord...@openssl.org
