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Improve documentation of signature verification process

cute-signatures
Reid Rankin 2020-01-23 16:11:03 +00:00 committed by Timo Teräs
parent 1f9e56d8a4
commit 093c4b8077
1 changed files with 19 additions and 7 deletions
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26
src/package.c
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@ -474,9 +474,14 @@ void apk_sign_ctx_init(struct apk_sign_ctx *ctx, int action,
ctx->action = action;
switch (action) {
case APK_SIGN_VERIFY:
/* If we're only verifing, we're going to start with a
* signature section, which we don't need a hash of */
ctx->md = EVP_md_null();
break;
case APK_SIGN_VERIFY_IDENTITY:
/* If we're checking the package against a particular hash,
* we need to start with that hash, because there may not
* be a signature section to deduce it from */
ctx->md = EVP_sha1();
memcpy(&ctx->identity, identity, sizeof(ctx->identity));
break;
@ -566,10 +571,10 @@ int apk_sign_ctx_process_file(struct apk_sign_ctx *ctx,
return 1;
}
/* A signature file */
/* By this point, we must be handling a signature file */
ctx->num_signatures++;
/* Found already a trusted key */
/* Already found a signature by a trusted key; no need to keep searching */
if ((ctx->action != APK_SIGN_VERIFY &&
ctx->action != APK_SIGN_VERIFY_AND_GENERATE) ||
ctx->signature.pkey != NULL)
@ -645,6 +650,12 @@ int apk_sign_ctx_verify_tar(void *sctx, const struct apk_file_info *fi,
return 0;
}
/* apk_sign_ctx_mpart_cb() handles hashing archives and checking signatures, but
it can't do it alone. apk_sign_ctx_process_file() must be in the loop to
actually select which signature is to be verified and load the corresponding
public key into the context object, and apk_sign_ctx_parse_pkginfo_line()
needs to be called when handling the .PKGINFO file to find any applicable
datahash and load it into the context for this function to check against. */
int apk_sign_ctx_mpart_cb(void *ctx, int part, apk_blob_t data)
{
struct apk_sign_ctx *sctx = (struct apk_sign_ctx *) ctx;
@ -671,14 +682,12 @@ int apk_sign_ctx_mpart_cb(void *ctx, int part, apk_blob_t data)
part != APK_MPART_END)
goto update_digest;
/* Drool in the remaining of the digest block now, we will finish
* it on all cases */
/* Drool in the remainder of the digest block now, we will finish
* hashing it in all cases */
EVP_DigestUpdate(sctx->mdctx, data.ptr, data.len);
/* End of control-block and checking control hash/signature or
* end of data-block and checking its hash/signature */
if (sctx->has_data_checksum && !end_of_control) {
/* End of control-block and check it's hash */
/* End of data-block with a checksum read from the control block */
EVP_DigestFinal_ex(sctx->mdctx, calculated, NULL);
if (EVP_MD_CTX_size(sctx->mdctx) == 0 ||
memcmp(calculated, sctx->data_checksum,
@ -691,6 +700,9 @@ int apk_sign_ctx_mpart_cb(void *ctx, int part, apk_blob_t data)
return 0;
}
/* Either end of control block with a data checksum or end
* of the data block following a control block without a data
* checksum. In either case, we're checking a signature. */
r = check_signing_key_trust(sctx);
if (r < 0)
return r;