diff options
Diffstat (limited to 'crypto/srp/srp_vfy.c')
-rw-r--r-- | crypto/srp/srp_vfy.c | 101 |
1 files changed, 95 insertions, 6 deletions
diff --git a/crypto/srp/srp_vfy.c b/crypto/srp/srp_vfy.c index 1eba5a7cb1..1bf2f267ed 100644 --- a/crypto/srp/srp_vfy.c +++ b/crypto/srp/srp_vfy.c @@ -26,6 +26,15 @@ # define MAX_LEN 2500 /* + * Note that SRP uses its own variant of base 64 encoding. A different base64 + * alphabet is used and no padding '=' characters are added. Instead we pad to + * the front with 0 bytes and subsequently strip off leading encoded padding. + * This variant is used for compatibility with other SRP implementations - + * notably libsrp, but also others. It is also required for backwards + * compatibility in order to load verifier files from other OpenSSL versions. + */ + +/* * Convert a base64 string into raw byte array representation. * Returns the length of the decoded data, or -1 on error. */ @@ -33,24 +42,79 @@ static int t_fromb64(unsigned char *a, size_t alen, const char *src) { EVP_ENCODE_CTX *ctx; int outl = 0, outl2 = 0; - size_t size = strlen(src); + size_t size, padsize; + const unsigned char *pad = (const unsigned char *)"00"; - if (size > INT_MAX) + while (*src == ' ' || *src == '\t' || *src == '\n') + ++src; + size = strlen(src); + padsize = 4 - (size & 3); + padsize &= 3; + + /* Four bytes in src become three bytes output. */ + if (size > INT_MAX || ((size + padsize) / 4) * 3 > alen) return -1; ctx = EVP_ENCODE_CTX_new(); if (ctx == NULL) return -1; + /* + * This should never occur because 1 byte of data always requires 2 bytes of + * encoding, i.e. + * 0 bytes unencoded = 0 bytes encoded + * 1 byte unencoded = 2 bytes encoded + * 2 bytes unencoded = 3 bytes encoded + * 3 bytes unencoded = 4 bytes encoded + * 4 bytes unencoded = 6 bytes encoded + * etc + */ + if (padsize == 3) + return -1; + + /* Valid padsize values are now 0, 1 or 2 */ + EVP_DecodeInit(ctx); - if (EVP_DecodeUpdate(ctx, a, &outl, (const unsigned char *)src, size) < 0) { + evp_encode_ctx_set_flags(ctx, EVP_ENCODE_CTX_USE_SRP_ALPHABET); + + /* Add any encoded padding that is required */ + if (padsize != 0 + && EVP_DecodeUpdate(ctx, a, &outl, pad, padsize) < 0) { EVP_ENCODE_CTX_free(ctx); return -1; } + if (EVP_DecodeUpdate(ctx, a, &outl2, (const unsigned char *)src, size) < 0) { + EVP_ENCODE_CTX_free(ctx); + return -1; + } + outl += outl2; EVP_DecodeFinal(ctx, a + outl, &outl2); + outl += outl2; + + /* Strip off the leading padding */ + if (padsize != 0) { + if ((int)padsize >= outl) + return -1; + /* + * If we added 1 byte of padding prior to encoding then we have 2 bytes + * of "real" data which gets spread across 4 encoded bytes like this: + * (6 bits pad)(2 bits pad | 4 bits data)(6 bits data)(6 bits data) + * So 1 byte of pre-encoding padding results in 1 full byte of encoded + * padding. + * If we added 2 bytes of padding prior to encoding this gets encoded + * as: + * (6 bits pad)(6 bits pad)(4 bits pad | 2 bits data)(6 bits data) + * So 2 bytes of pre-encoding padding results in 2 full bytes of encoded + * padding, i.e. we have to strip the same number of bytes of padding + * from the encoded data as we added to the pre-encoded data. + */ + memmove(a, a + padsize, outl - padsize); + outl -= padsize; + } EVP_ENCODE_CTX_free(ctx); - return outl + outl2; + + return outl; } /* @@ -61,18 +125,43 @@ static int t_tob64(char *dst, const unsigned char *src, int size) { EVP_ENCODE_CTX *ctx = EVP_ENCODE_CTX_new(); int outl = 0, outl2 = 0; + unsigned char pad[2] = {0, 0}; + size_t leadz = 0; if (ctx == NULL) return 0; EVP_EncodeInit(ctx); - evp_encode_ctx_set_flags(ctx, EVP_ENCODE_CTX_NO_NEWLINES); + evp_encode_ctx_set_flags(ctx, EVP_ENCODE_CTX_NO_NEWLINES + | EVP_ENCODE_CTX_USE_SRP_ALPHABET); - if (!EVP_EncodeUpdate(ctx, (unsigned char *)dst, &outl, src, size)) { + /* + * We pad at the front with zero bytes until the length is a multiple of 3 + * so that EVP_EncodeUpdate/EVP_EncodeFinal does not add any of its own "=" + * padding + */ + leadz = 3 - (size % 3); + if (leadz != 3 + && !EVP_EncodeUpdate(ctx, (unsigned char *)dst, &outl, pad, + leadz)) { EVP_ENCODE_CTX_free(ctx); return 0; } + + if (!EVP_EncodeUpdate(ctx, (unsigned char *)dst + outl, &outl2, src, + size)) { + EVP_ENCODE_CTX_free(ctx); + return 0; + } + outl += outl2; EVP_EncodeFinal(ctx, (unsigned char *)dst + outl, &outl2); + outl += outl2; + + /* Strip the encoded padding at the front */ + if (leadz != 3) { + memmove(dst, dst + leadz, outl - leadz); + dst[outl - leadz] = '\0'; + } EVP_ENCODE_CTX_free(ctx); return 1; |