Signing two times with same contex?

[Pablo J. Royo]

Hi:   I need to sign files with two different private keys (two signers).Files are quite big and I dont want to read the whole file each time a signer may sign, because the digest its the same for every one. So I´d like to call EVP_SignInit( ctx ), EVP_SignUpdate(ctx) (this as not EOF) ... only one time, and then issue a EVP_SignFinal(ctx,PrivateKey..) for each new sign. I´ve modified the demos/sign.c file to do this, but the second sign is never good, which I think is becuse something in the contex (ctx is a struct EVP_MD_CTX ) is beeing changed after the first sign process.   Could I use a fresh copy of contex for each new EVP_SignFinal ? Is there any function to safely copy the contex for later use ? I´d like another solution, but...   Thanks. ( and sorry for my poor english)