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RSA PSS: fix first byte check for keys of size 8N+1

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For a key of size 8N+1, check that the first byte after applying the
public key operation is 0 (it could have been 1 instead). The code was
incorrectly doing a no-op check instead, which led to invalid
signatures being accepted. Not a security flaw, since you would need the
private key to craft such an invalid signature, but a bug nonetheless.
This commit is contained in:
Gilles Peskine 2017-10-19 15:23:49 +02:00
parent 139108af94
commit b00b0da452
2 changed files with 11 additions and 3 deletions
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6
library/rsa.c
View file

@ -1371,15 +1371,15 @@ int mbedtls_rsa_rsassa_pss_verify_ext( mbedtls_rsa_context *ctx,
*/
msb = mbedtls_mpi_bitlen( &ctx->N ) - 1;
if( buf[0] >> ( 8 - siglen * 8 + msb ) )
return( MBEDTLS_ERR_RSA_BAD_INPUT_DATA );
/* Compensate for boundary condition when applying mask */
if( msb % 8 == 0 )
{
p++;
siglen -= 1;
}
else
if( buf[0] >> ( 8 - siglen * 8 + msb ) )
return( MBEDTLS_ERR_RSA_BAD_INPUT_DATA );
if( siglen < hlen + 2 )
return( MBEDTLS_ERR_RSA_BAD_INPUT_DATA );

8
tests/suites/test_suite_pkcs1_v21.data
View file

@ -819,6 +819,14 @@ RSASSA-PSS verify ext, 521-bit key, SHA-512, empty salt, bad signature
depends_on:MBEDTLS_SHA512_C
pkcs1_rsassa_pss_verify_ext:521:16:"0131b69860f3cb9bf85ea358fdf2bd2990f1b77a80d6a4fdf817a43dd896bdf7dd26af8ac0237f526e0d33b105c971fdbd4ffa9ece99fc469f31ecf429e8f562c1c3":16:"010001":MBEDTLS_MD_SHA512:MBEDTLS_MD_SHA512:MBEDTLS_MD_SHA512:0:"":"00471794655837da498cbf27242807b40593a353c707eb22fd2cc5a3259e728ac4f1df676043eeec8e16c1175b3d9ac8cae72ec1d5772dd69de71c5677f19031568e":MBEDTLS_ERR_RSA_BAD_INPUT_DATA:MBEDTLS_ERR_RSA_BAD_INPUT_DATA
RSASSA-PSS verify ext, 521-bit key, SHA-256, empty salt, good signature
depends_on:MBEDTLS_SHA256_C
pkcs1_rsassa_pss_verify_ext:521:16:"0131b69860f3cb9bf85ea358fdf2bd2990f1b77a80d6a4fdf817a43dd896bdf7dd26af8ac0237f526e0d33b105c971fdbd4ffa9ece99fc469f31ecf429e8f562c1c3":16:"010001":MBEDTLS_MD_SHA256:MBEDTLS_MD_SHA256:MBEDTLS_MD_SHA256:0:"41":"009c4941157fa36288e467310b198ab0c615c40963d611ffeef03000549ded809235955ecc57adba44782e9497c004f480ba2b3d58db8335fe0b391075c02c843a6d":0:0
RSASSA-PSS verify ext, 521-bit key, SHA-256, empty salt, flipped-highest-bit signature
depends_on:MBEDTLS_SHA256_C
pkcs1_rsassa_pss_verify_ext:521:16:"0131b69860f3cb9bf85ea358fdf2bd2990f1b77a80d6a4fdf817a43dd896bdf7dd26af8ac0237f526e0d33b105c971fdbd4ffa9ece99fc469f31ecf429e8f562c1c3":16:"010001":MBEDTLS_MD_SHA256:MBEDTLS_MD_SHA256:MBEDTLS_MD_SHA256:0:"41":"00e11a2403df681c44a1f73f014b6c9ad17847d0b673f7c2a801cee208d10ab5792c10cd0cd495a4b331aaa521409fca7cb1b0d978b3a84cd67e28078b98753e9466":MBEDTLS_ERR_RSA_BAD_INPUT_DATA:MBEDTLS_ERR_RSA_BAD_INPUT_DATA
RSASSA-PSS verify ext, all-zero padding, automatic salt length
depends_on:MBEDTLS_SHA256_C
pkcs1_rsassa_pss_verify_ext:512:16:"00b076d23250816f9aab02307e452b97f0cae7598369b41624e8afc7971a59a13892f64b07eaa6ec928c160b2d6ec8f9d0dd5b63c8b3ac0767b4f65c892f56c10f":16:"010001":MBEDTLS_MD_NONE:MBEDTLS_MD_SHA256:MBEDTLS_MD_SHA256:MBEDTLS_RSA_SALT_LEN_ANY:"":"63a35294577c7e593170378175b7df27c293dae583ec2a971426eb2d66f2af483e897bfae5dc20300a9d61a3644e08c3aee61a463690a3498901563c46041056":MBEDTLS_ERR_RSA_INVALID_PADDING:MBEDTLS_ERR_RSA_INVALID_PADDING